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Summarize the following historical passage: | Life Processes
87
5.3 RESPIR
5.3 RESPIR
5.3 RESPIR
5.3 RESPIR
5.3 RESPIRAAAAATION
TION
TION
TION
TION
Activity 5.4
Activity 5.4
Activity 5.4
Activity 5.4
Activity 5.4
n
Take some freshly prepared lime
water in a test tube.
n
Blow air through this lime water.
n
Note how long it takes for the lime
water to turn milky.
n
Use a syringe or pichkari to pass air
through some fresh lime water
taken in another test tube (Fig. 5.7).
n
Note how long it takes for this lime
water to turn milky.
n
What does this tell us about the
amount of carbon dioxide in the air
that we breathe out?
1.
What are the differences between autotrophic nutrition and heterotrophic
nutrition?
2.
Where do plants get each of the raw materials required for photosynthesis?
3.
What is the role of the acid in our stomach?
4.
What is the function of digestive enzymes?
5.
How is the small intestine designed to absorb digested food?
Tube
Test tube containing
lime water
Lime
water
Rubber
tube
(a)
(b)
Pichkari
Q
U
E
S
T
I
O
N
S
?
Activity 5.5
Activity 5.5
Activity 5.5
Activity 5.5
Activity 5.5
n
Take some fruit juice or sugar solution and add some yeast to
this. Take this mixture in a test tube fitted with a one-holed cork.
n
Fit the cork with a bent glass tube. Dip the free end of the glass
tube into a test tube containing freshly prepared lime water.
n
What change is observed in the lime water and how long does it
take for this change to occur?
n
What does this tell us about the products of fermentation?
We have discussed nutrition in organisms in the last section. The
food material taken in during the process of nutrition is used in cells to
provide energy for various life processes. Diverse organisms do this in
different ways – some use oxygen to break-down glucose completely
into carbon dioxide and water, some use other pathways that do not
involve oxygen (Fig. 5.8). In all cases, the first step is the break-down of
glucose, a six-carbon molecule, into a three-carbon molecule called
pyruvate. This process takes place in the cytoplasm. Further, the
pyruvate may be converted into ethanol and carbon dioxide. This process
takes place in yeast during fermentation. Since this process takes place
in the absence of air (oxygen), it is called anaerobic respiration. Break-
down of pyruvate using oxygen takes place in the mitochondria. This
Figure 5.7
Figure 5.7
Figure 5.7
Figure 5.7
Figure 5.7
(a) Air being passed into lime water with a pichkari/
syringe, (b) air being exhaled into lime water
2024-25 | Life Processes 87 5.3 RESPIR 5.3 RESPIR 5.3 RESPIR 5.3 RESPIR 5.3 RESPIRAAAAATION TION TION TION TION Activity 5.4 Activity 5.4 Activity 5.4 Activity 5.4 Activity 5.4 n Take some freshly prepared lime water in a test tube. n Blow air through this lime water. n Note how long it... |
Summarize the following historical passage: | Science
100
Control and
Coordination
6
CHAPTER
I
n the previous chapter, we looked at life processes involved in the
maintenance functions in living organisms. There, we had started with
a notion we all have, that if we see something moving, it is alive. Some of
these movements are in fact the result of growth, as in plants. A seed
germinates and grows, and we can see that the seedling moves over the
course of a few days, it pushes soil aside and comes out. But if its growth
were to be stopped, these movements would not happen. Some
movements, as in many animals and some plants, are not connected
with growth. A cat running, children playing on swings, buffaloes
chewing cud – these are not movements caused by growth.
Why do we associate such visible movements with life? A possible
answer is that we think of movement as a response to a change in the
environment of the organism. The cat may be running because it has
seen a mouse. Not only that, we also think of movement as an attempt
by living organisms to use changes in their environment to their
advantage. Plants grow out into the sunshine. Children try to get pleasure
and fun out of swinging. Buffaloes chew cud to help break up tough
food so as to be able to digest it better. When bright light is focussed on
our eyes or when we touch a hot object, we detect the change and respond
to it with movement in order to protect ourselves.
If we think a bit more about this, it becomes apparent that all this
movement, in response to the environment, is carefully controlled. Each
kind of a change in the environment evokes an appropriate movement
in response. When we want to talk to our friends in class, we whisper,
rather than shouting loudly. Clearly, the movement to be made depends
on the event that is triggering it. Therefore, such controlled movement
must be connected to the recognition of various events in the
environment, followed by only the correct movement in response. In other
words, living organisms must use systems providing control and
coordination. In keeping with the general principles of body organisation
in multicellular organisms, specialised tissues are used to provide these
control and coordination activities.
6.1
6.1
6.1
6.1
6.1 ANIMALS – NERVOUS SYSTEM
ANIMALS – NERVOUS SYSTEM
ANIMALS – NERVOUS SYSTEM
ANIMALS – NERVOUS SYSTEM
ANIMALS – NERVOUS SYSTEM
In animals, such control and coordination are provided by nervous and
muscular tissues, which we have studied in Class IX. Touching a hot
2024-25 | Science 100 Control and Coordination 6 CHAPTER I n the previous chapter, we looked at life processes involved in the maintenance functions in living organisms. There, we had started with a notion we all have, that if we see something moving, it is alive. Some of these movements are in... |
Summarize the following historical passage: | Science
140
Figure 9.7
Figure 9.7
Figure 9.7
Figure 9.7
Figure 9.7 Ray diagrams for the image formation by a concave mirror
Activity 9.4
Activity 9.4
Activity 9.4
Activity 9.4
Activity 9.4
n
Draw neat ray diagrams for each position of the object shown in
Table 9.1.
n
You may take any two of the rays mentioned in the previous section
for locating the image.
n
Compare your diagram with those given in Fig. 9.7.
n
Describe the nature, position and relative size of the image formed
in each case.
n
Tabulate the results in a convenient format.
Uses of concave mirrors
Concave mirrors are commonly used in torches, search-lights and
vehicles headlights to get powerful parallel beams of light. They are
often used as shaving mirrors to see a larger image of the face. The
dentists use concave mirrors to see large images of the teeth of patients.
Large concave mirrors are used to concentrate sunlight to produce
heat in solar furnaces.
(b)
Image formation by a Convex Mirror
We studied the image formation by a concave mirror. Now we shall
study the formation of image by a convex mirror.
2024-25 | Science 140 Figure 9.7 Figure 9.7 Figure 9.7 Figure 9.7 Figure 9.7 Ray diagrams for the image formation by a concave mirror Activity 9.4 Activity 9.4 Activity 9.4 Activity 9.4 Activity 9.4 n Draw neat ray diagrams for each position of the object shown in Table 9.1. n You may... |
Summarize the following historical passage: | Science
6
1.2 TYPES OF CHEMIC
1.2 TYPES OF CHEMIC
1.2 TYPES OF CHEMIC
1.2 TYPES OF CHEMIC
1.2 TYPES OF CHEMICAL REA
AL REA
AL REA
AL REA
AL REACTIONS
CTIONS
CTIONS
CTIONS
CTIONS
We have learnt in Class IX that during a chemical reaction atoms of one
element do not change into those of another element. Nor do atoms
disappear from the mixture or appear from elsewhere. Actually, chemical
reactions involve the breaking and making of bonds between atoms to
produce new substances. You will study about types of bonds formed
between atoms in Chapters 3 and 4.
1.2.1 Combination Reaction
Activity 1.4
Activity 1.4
Activity 1.4
Activity 1.4
Activity 1.4
n
Take a small amount of calcium oxide
or quick lime in a beaker.
n
Slowly add water to this.
n
Touch the beaker as shown in Fig. 1.3.
n
Do you feel any change in temperature?
Figure 1.3
Figure 1.3
Figure 1.3
Figure 1.3
Figure 1.3
Formation of slaked
lime by the reaction of
calcium oxide with
water
Calcium oxide reacts vigorously with water to produce slaked lime
(calcium hydroxide) releasing a large amount of heat.
CaO(s)
+
H2O(l) → Ca(OH)2(aq) + Heat
(1.13)
(Quick lime)
(Slaked lime)
In this reaction, calcium oxide and water combine to form a single
product, calcium hydroxide. Such a reaction in which a single product
is formed from two or more reactants is known as a combination reaction.
Q
U
E
S
T
I
O
N
S
1.
Why should a magnesium ribbon be cleaned before burning in air?
2.
Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate +
Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
3.
Write a balanced chemical equation with state symbols for the
following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react
to give insoluble barium sulphate and the solution of sodium
chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric
acid solution (in water) to produce sodium chloride solution and
water.
?
2024-25 | Science 6 1.2 TYPES OF CHEMIC 1.2 TYPES OF CHEMIC 1.2 TYPES OF CHEMIC 1.2 TYPES OF CHEMIC 1.2 TYPES OF CHEMICAL REA AL REA AL REA AL REA AL REACTIONS CTIONS CTIONS CTIONS CTIONS We have learnt in Class IX that during a chemical reaction atoms of one element... |
Summarize the following historical passage: | Chemical Reactions
and Equations
1
CHAPTER
C
onsider the following situations of daily life and think what happens
when –
n
milk is left at room temperature during summers.
n
an iron tawa/pan/nail is left exposed to humid atmosphere.
n
grapes get fermented.
n
food is cooked.
n
food gets digested in our body.
n
we respire.
In all the above situations, the nature and the identity of the initial
substance have somewhat changed. We have already learnt about physical
and chemical changes of matter in our previous classes. Whenever a chemical
change occurs, we can say that a chemical reaction has taken place.
You may perhaps be wondering as to what is actually meant by a
chemical reaction. How do we come to know that a chemical reaction
has taken place? Let us perform some activities to find the answer to
these questions.
Figure 1.1
Burning of a magnesium ribbon in air and collection of magnesium
oxide in a watch-glass
Activity 1.1
Activity 1.1
Activity 1.1
Activity 1.1
Activity 1.1
CAUTION: This Activity needs
the teacher’s assistance. It
would be better if students
wear suitable eyeglasses.
n
Clean a magnesium ribbon
about 3-4 cm long by rubbing
it with sandpaper.
n
Hold it with a pair of tongs.
Burn it using a spirit lamp or
burner and collect the ash so
formed in a watch-glass as
shown in Fig. 1.1. Burn the
magnesium ribbon keeping it
away as far as possible from
your eyes.
n
What do you observe?
“Facts are not science — as the dictionary is not literature.”
Martin H. Fischer
2024-25 | Chemical Reactions and Equations 1 CHAPTER C onsider the following situations of daily life and think what happens when – n milk is left at room temperature during summers. n an iron tawa/pan/nail is left exposed to humid atmosphere. n grapes get fermented. n food is cooked. n food gets... |
Summarize the following historical passage: | How do Organisms
Reproduce?
7
CHAPTER
B
efore we discuss the mechanisms by which organisms reproduce,
let us ask a more basic question – why do organisms reproduce?
After all, reproduction is not necessary to maintain the life of an individual
organism, unlike the essential life processes such as nutrition,
respiration, or excretion. On the other hand, if an individual organism is
going to create more individuals, a lot of its energy will be spent in the
process. So why should an individual organism waste energy on a process
it does not need to stay alive? It would be interesting to discuss the
possible answers in the classroom!
Whatever the answer to this question, it is obvious that we notice
organisms because they reproduce. If there were to be only one, non-
reproducing member of a particular kind, it is doubtful that we would
have noticed its existence. It is the large numbers of organisms belonging
to a single species that bring them to our notice. How do we know that
two different individual organisms belong to the same species? Usually,
we say this because they look similar to each other. Thus, reproducing
organisms create new individuals that look very much like themselves.
7.1 DO ORG
7.1 DO ORG
7.1 DO ORG
7.1 DO ORG
7.1 DO ORGANISMS CREA
ANISMS CREA
ANISMS CREA
ANISMS CREA
ANISMS CREATE EXA
TE EXA
TE EXA
TE EXA
TE EXACT COPIES OF
CT COPIES OF
CT COPIES OF
CT COPIES OF
CT COPIES OF
THEMSEL
THEMSEL
THEMSEL
THEMSEL
THEMSELVES?
VES?
VES?
VES?
VES?
Organisms look similar because their body designs are similar. If body
designs are to be similar, the blueprints for these designs should be
similar. Thus, reproduction at its most basic level will involve making
copies of the blueprints of body design. In Class IX, we learnt that the
chromosomes in the nucleus of a cell contain information for inheritance
of features from parents to next generation in the form of DNA (Deoxyribo
Nucleic Acid) molecules. The DNA in the cell nucleus is the information
source for making proteins. If the information is changed, different
proteins will be made. Different proteins will eventually lead to altered
body designs.
Therefore, a basic event in reproduction is the creation of a DNA
copy. Cells use chemical reactions to build copies of their DNA. This
creates two copies of the DNA in a reproducing cell, and they will need to
be separated from each other. However, keeping one copy of DNA in the
original cell and simply pushing the other one out would not work,
2024-25 | How do Organisms Reproduce? 7 CHAPTER B efore we discuss the mechanisms by which organisms reproduce, let us ask a more basic question – why do organisms reproduce? After all, reproduction is not necessary to maintain the life of an individual organism, unlike the essential life processes such as nutrition,... |
Summarize the following historical passage: | Acids, Bases and Salts
35
8. Why do acids not show acidic behaviour in the absence of water?
9. Five solutions A,B,C,D and E when tested with universal indicator showed pH as
4,1,11,7 and 9, respectively. Which solution is
(a)
neutral?
(b)
strongly alkaline?
(c)
strongly acidic?
(d)
weakly acidic?
(e)
weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric
acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test
tube B. Amount and concentration taken for both the acids are same. In which test
tube will the fizzing occur more vigorously and why?
11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into
curd? Explain your answer.
12. A milkman adds a very small amount of baking soda to fresh milk.
(a)
Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b)
Why does this milk take a long time to set as curd?
13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
14. What is a neutralisation reaction? Give two examples.
15. Give two important uses of washing soda and baking soda.
(I) Prepare your own indicator
n
Crush beetroot in a mortar.
n
Add sufficient water to obtain the extract.
n
Filter the extract by the procedure learnt by you in earlier classes.
n
Collect the filtrate to test the substances you may have tasted earlier.
n
Arrange four test tubes in a test tube stand and label them as A,B,C and D. Pour
2 mL each of lemon juice solution, soda-water, vinegar and baking soda solution
in them respectively.
n
Put 2-3 drops of the beetroot extract in each test tube and note the colour change
if any. Write your observation in a Table.
n
You can prepare indicators by using other natural materials like extracts of red
cabbage leaves, coloured petals of some flowers such as Petunia, Hydrangea and
Geranium.
Group Activity
2024-25 | Acids, Bases and Salts 35 8. Why do acids not show acidic behaviour in the absence of water? 9. Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is (a) neutral? (b) strongly alkaline? (c) strongly acidic? (d) weakly acidic?... |
Summarize the following historical passage: | Science
168
Figure 10.10
Figure 10.10
Figure 10.10
Figure 10.10
Figure 10.10
Atmospheric refraction
effects at sunrise and
sunset
10.5 ATMOSPHERIC REFRACTION
You might have observed the apparent random wavering or
flickering of objects seen through a turbulent stream of hot air
rising above a fire or a radiator. The air just above the fire becomes
hotter than the air further up. The hotter air is lighter (less dense)
than the cooler air above it, and has a refractive index slightly
less than that of the cooler air. Since the physical conditions of
the refracting medium (air) are not stationary, the apparent
position of the object, as seen through the hot air, fluctuates.
This wavering is thus an effect of atmospheric refraction (refraction
of light by the earth’s atmosphere) on a small scale in our local
environment. The twinkling of stars is a similar phenomenon on
a much larger scale. Let us see how we can explain it.
Twinkling of stars
The twinkling of a star is due to atmospheric refraction of starlight. The
starlight, on entering the earth’s atmosphere, undergoes refraction
continuously before it reaches the earth. The atmospheric refraction
occurs in a medium of gradually changing refractive index. Since the
atmosphere bends starlight towards the normal, the apparent position
of the star is slightly different from its actual position. The star appears
slightly higher (above) than its actual position when viewed near the
horizon (Fig. 10.9). Further, this apparent position of the star is not
stationary, but keeps on changing slightly, since the physical conditions
of the earth’s atmosphere are not stationary, as was the case in the
previous paragraph. Since the stars are very distant, they approximate
point-sized sources of light. As the path of rays of light coming from
the star goes on varying slightly, the apparent position of the star
fluctuates and the amount of starlight entering the eye flickers – the
star sometimes appears brighter, and at some other time, fainter, which
is the twinkling effect.
Why don’t the planets twinkle? The planets are much
closer to the earth, and are thus seen as extended sources.
If we consider a planet as a collection of a large number
of point-sized sources of light, the total variation in the
amount of light entering our eye from all the individual
point-sized sources will average out to zero, thereby
nullifying the twinkling effect.
Advance sunrise and delayed sunset
The Sun is visible to us about 2 minutes before the actual
sunrise, and about 2 minutes after the actual sunset
because of atmospheric refraction. By actual sunrise, we
mean the actual crossing of the horizon by the Sun. Fig.
10.10 shows the actual and apparent positions of the
Sun with respect to the horizon. The time difference
between actual sunset and the apparent sunset is about
2 minutes. The apparent flattening of the Sun’s disc at
sunrise and sunset is also due to the same phenomenon.
Figure 10.9
Figure 10.9
Figure 10.9
Figure 10.9
Figure 10.9
Apparent star position
due to atmospheric
refraction
2024-25 | Science 168 Figure 10.10 Figure 10.10 Figure 10.10 Figure 10.10 Figure 10.10 Atmospheric refraction effects at sunrise and sunset 10.5 ATMOSPHERIC REFRACTION You might have observed the apparent random wavering or flickering of objects seen through a turbulent stream of hot air rising above a fire or a radiator. The... |
Summarize the following historical passage: | Electricity
175
11.4 OHM’S LA
11.4 OHM’S LA
11.4 OHM’S LA
11.4 OHM’S LA
11.4 OHM’S LAW
WW
WW
Is there a relationship between the potential difference across a conductor
and the current through it? Let us explore with an Activity.
Activity 11.1
Activity 11.1
Activity 11.1
Activity 11.1
Activity 11.1
n
Set up a circuit as shown in Fig. 11.2,
consisting of a nichrome wire XY of length,
say 0.5 m, an ammeter, a voltmeter and
four cells of 1.5 V each. (Nichrome is an
alloy of nickel, chromium, manganese, and
iron metals.)
n
First use only one cell as the source in the
circuit. Note the reading in the ammeter I,
for the current and reading of the voltmeter
V for the potential difference across the
nichrome wire XY in the circuit. Tabulate
them in the Table given.
n
Next connect two cells in the circuit and
note the respective readings of the ammeter and voltmeter for the values of current through
the nichrome wire and potential difference across the nichrome wire.
n
Repeat the above steps using three cells and then four cells in the circuit separately.
n
Calculate the ratio of V to I for each pair of potential difference V and current I.
S.
Number of cells
Current through
Potential difference
V/I
No.
used in the
the nichrome
across the
(volt/ampere)
circuit
wire, I
nichrome
(ampere)
wire, V (volt)
1
1
2
2
3
3
4
4
n
Plot a graph between V and I, and observe the nature of the graph.
7
Electric bulb
or
8
A resistor of resistance R
9
Variable resistance or rheostat
or
10
Ammeter
11
Voltmeter
Figure 11.2
Figure 11.2
Figure 11.2
Figure 11.2
Figure 11.2 Electric circuit for studying Ohm’s law
2024-25 | Electricity 175 11.4 OHM’S LA 11.4 OHM’S LA 11.4 OHM’S LA 11.4 OHM’S LA 11.4 OHM’S LAW WW WW Is there a relationship between the potential difference across a conductor and the current through it? Let us explore with an Activity. Activity 11.1 Activity 11.1 Activity 11.1 Activity 11.1 Activity... |
Summarize the following historical passage: | Control and Coordination
101
object is an urgent and dangerous
situation for us. We need to detect it,
and respond to it. How do we detect that
we are touching a hot object? All
information from our environment is
detected by the specialised tips of some
nerve cells. These receptors are usually
located in our sense organs, such as the
inner ear, the nose, the tongue, and so
on. So gustatory receptors will detect taste
while olfactory receptors will detect smell.
This information, acquired at the
end of the dendritic tip of a nerve cell
[Fig. 6.1 (a)], sets off a chemical reaction
that creates an electrical impulse. This
impulse travels from the dendrite to the
cell body, and then along the axon to its
end. At the end of the axon, the electrical
impulse sets off the release of some
chemicals. These chemicals cross the
gap, or synapse, and start a similar
electrical impulse in a dendrite of the next
neuron. This is a general scheme of how
nervous impulses travel in the body. A
similar synapse finally allows delivery of such impulses from neurons to
other cells, such as muscles cells or gland [Fig. 6.1 (b)].
It is thus no surprise that nervous tissue is made up of an organised
network of nerve cells or neurons, and is specialised for conducting
information via electrical impulses from one part of the body to another.
Look at Fig. 6.1 (a) and identify the parts of a neuron (i) where
information is acquired, (ii) through which information travels as an
electrical impulse, and (iii) where this impulse must be converted into a
chemical signal for onward transmission.
Activity 6.1
Activity 6.1
Activity 6.1
Activity 6.1
Activity 6.1
n
Put some sugar in your mouth. How does it taste?
n
Block your nose by pressing it between your thumb and index
finger. Now eat sugar again. Is there any difference in its taste?
n
While eating lunch, block your nose in the same way and notice if
you can fully appreciate the taste of the food you are eating.
Is there a difference in how sugar and food taste if your nose is
blocked? If so, why might this be happening? Read and talk about
possible explanations for these kinds of differences. Do you come across
a similar situation when you have a cold?
Figure 6.1
Figure 6.1
Figure 6.1
Figure 6.1
Figure 6.1 (a) Structure of neuron, (b) Neuromuscular
junction
(a)
(b)
2024-25 | Control and Coordination 101 object is an urgent and dangerous situation for us. We need to detect it, and respond to it. How do we detect that we are touching a hot object? All information from our environment is detected by the specialised tips of some nerve cells. These receptors... |
Summarize the following historical passage: | Science
56
n
Non-metals form negatively charged ions by gaining electrons when reacting with
metals.
n
Non-metals form oxides which are either acidic or neutral.
n
Non-metals do not displace hydrogen from dilute acids. They react with hydrogen
to form hydrides.
E
X
E
R
C
I
S
E
S
1.
Which of the following pairs will give displacement reactions?
(a)
NaCl solution and copper metal
(b)
MgCl2 solution and aluminium metal
(c)
FeSO4 solution and silver metal
(d)
AgNO3 solution and copper metal.
2.
Which of the following methods is suitable for preventing an iron frying pan from
rusting?
(a)
Applying grease
(b)
Applying paint
(c)
Applying a coating of zinc
(d)
All of the above.
3.
An element reacts with oxygen to give a compound with a high melting point. This
compound is also soluble in water. The element is likely to be
(a)
calcium
(b)
carbon
(c)
silicon
(d)
iron.
4.
Food cans are coated with tin and not with zinc because
(a)
zinc is costlier than tin.
(b)
zinc has a higher melting point than tin.
(c)
zinc is more reactive than tin.
(d)
zinc is less reactive than tin.
5.
You are given a hammer, a battery, a bulb, wires and a switch.
(a)
How could you use them to distinguish between samples of metals and
non-metals?
(b)
Assess the usefulness of these tests in distinguishing between metals and
non-metals.
6.
What are amphoteric oxides? Give two examples of amphoteric oxides.
7.
Name two metals which will displace hydrogen from dilute acids, and two metals
which will not.
2024-25 | Science 56 n Non-metals form negatively charged ions by gaining electrons when reacting with metals. n Non-metals form oxides which are either acidic or neutral. n Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides. E X E R C I S E S... |
Summarize the following historical passage: | Life Processes
97
like in the lungs, is a cluster of very thin-walled blood
capillaries. Each capillary cluster in the kidney is
associated with the cup-shaped end of a coiled tube
called Bowman’s capsule that collects the filtrate
(Fig. 5.14). Each kidney has large numbers of these
filtration units called nephrons packed close together.
Some substances in the initial filtrate, such as glucose,
amino acids, salts and a major amount of water, are
selectively re-absorbed as the urine flows along the tube.
The amount of water re-absorbed depends on how much
excess water there is in the body, and on how much of
dissolved waste there is to be excreted. The urine forming
in each kidney eventually enters a long tube, the ureter,
which connects the kidneys with the urinary bladder.
Urine is stored in the urinary bladder until the pressure
of the expanded bladder leads to the urge to pass it out
through the urethra. The bladder is muscular, so it is
under nervous control, as we have discussed elsewhere.
As a result, we can usually control the urge to urinate.
More to Know!
Artificial kidney (Hemodialysis)
Kidneys are vital organs for survival. Several factors like infections, injury or restricted
blood flow to kidneys reduce the activity of kidneys. This leads to accumulation of
poisonous wastes in the body, which can even lead to death. In case of kidney
failure, an artificial kidney can be used. An artificial kidney is a device to remove
nitrogenous waste products from the blood through dialysis.
Artificial kidneys contain a number of tubes with a semi-permeable lining, suspended
in a tank filled with dialysing fluid.
This fluid has the same osmotic
pressure as blood, except that it is
devoid of nitrogenous wastes. The
patient’s blood is passed through
these tubes. During this passage,
the waste products from the blood
pass into dialysing fluid by diffusion.
The purified blood is pumped back
into the patient. This is similar to the
function of the kidney, but it is
different since there is no re-
absorption involved. Normally, in a
healthy adult, the initial filtrate in the
kidneys is about 180 L daily.
However, the volume actually
excreted is only a litre or two a day,
because the remaining filtrate is re-
absorbed in the kidney tubules.
Figure 5.14
Figure 5.14
Figure 5.14
Figure 5.14
Figure 5.14
Structure of a nephron
2024-25 | Life Processes 97 like in the lungs, is a cluster of very thin-walled blood capillaries. Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman’s capsule that collects the filtrate (Fig. 5.14). Each kidney has large numbers of these filtration units called... |
Summarize the following historical passage: | (viii)
This book has been made possible because of the active participation of many
people. I wish to thank Professor Krishna Kumar, Director, NCERT, Prof. G. Ravindra,
Joint Director, NCERT, and Professor Hukum Singh, Head, Department of Education
in Science and Mathematics, NCERT, specially for their keen interest in the development
of the book and for all the administrative support. I wish to put on record my sincere
appreciation for Dr Anjni Koul, the member-coordinator of the textbook development
committee, for her extraordinary commitment and efficiency. It has been a real pleasure
working with my textbook development team and the review committee. The chosen
editorial team worked extremely hard, on tight deadlines, to bring the book close to
the shape that we dreamt of. Fruitful discussions with some members of the MHRD
Monitoring Committee helped in providing the final touches to the book. I do not have
the words to acknowledge the professional and personal inputs I received from some
of my close friends during the preparation of this book. We warmly welcome comments
and suggestions for improvement from our readers.
RUPAMANJARI GHOSH
Professor of Physics
School of Physical Sciences
Jawaharlal Nehru University
New Delhi
2024-25 | (viii) This book has been made possible because of the active participation of many people. I wish to thank Professor Krishna Kumar, Director, NCERT, Prof. G. Ravindra, Joint Director, NCERT, and Professor Hukum Singh, Head, Department of Education in Science and Mathematics, NCERT, specially for their keen interest in the... |
Summarize the following historical passage: | Science
198
12.2.1 Magnetic Field due to a Current through a Straight
Conductor
What determines the pattern of the magnetic field generated by a current
through a conductor? Does the pattern depend on the shape of the
conductor? We shall investigate this with an activity.
We shall first consider the pattern of the magnetic field around a
straight conductor carrying current.
Activity 12.4
Activity 12.4
Activity 12.4
Activity 12.4
Activity 12.4
n
Take a long straight copper wire, two or three cells of 1.5 V each, and a plug key. Connect
all of them in series as shown in Fig. 12.5 (a).
n
Place the straight wire parallel to and over a compass needle.
n
Plug the key in the circuit.
n
Observe the direction of deflection of the north pole of the needle. If the current flows from
north to south, as shown in Fig. 12.5 (a), the north pole of the compass needle would move
towards the east.
n
Replace the cell connections in the circuit as shown in Fig. 12.5 (b). This would result in
the change of the direction of current through the copper wire, that is, from south to
north.
n
Observe the change in the direction of deflection of the needle. You will see that now the
needle moves in opposite direction, that is, towards the west [Fig. 12.5 (b)]. It means that
the direction of magnetic field produced by the electric current is also reversed.
Figure 12.5
Figure 12.5
Figure 12.5
Figure 12.5
Figure 12.5 A simple electric circuit in which a straight copper wire is placed parallel to and over a compass
needle. The deflection in the needle becomes opposite when the direction of the current is reversed.
(a)
(b)
Activity 12.5
Activity 12.5
Activity 12.5
Activity 12.5
Activity 12.5
n
Take a battery (12 V), a variable resistance (or a rheostat), an
ammeter (0–5 A), a plug key, connecting wires and a long straight
thick copper wire.
n
Insert the thick wire through the centre, normal to the plane of a
rectangular cardboard. Take care that the cardboard is fixed and
does not slide up or down.
2024-25 | Science 198 12.2.1 Magnetic Field due to a Current through a Straight Conductor What determines the pattern of the magnetic field generated by a current through a conductor? Does the pattern depend on the shape of the conductor? We shall investigate this with an activity. We shall first consider the... |
Summarize the following historical passage: | Light – Reflection and Refraction
147
In this Activity, you will note, the light ray has changed its direction
at points O and O′. Note that both the points O and O′ lie on surfaces
separating two transparent media. Draw a perpendicular NN’ to AB at O
and another perpendicular MM′ to CD at O′. The light ray at point O has
entered from a rarer medium to a denser medium, that is, from air to
glass. Note that the light ray has bent towards
the normal. At O′, the light ray has entered
from glass to air, that is, from a denser
medium to a rarer medium. The light here
has bent away from the normal. Compare the
angle of incidence with the angle of refraction
at both refracting surfaces AB and CD.
In Fig. 9.10, a ray EO is obliquely
incident on surface AB, called incident ray.
OO′ is the refracted ray and O′ H is the
emergent ray. You may observe that the
emergent ray is parallel to the direction of
the incident ray. Why does it happen so? The
extent of bending of the ray of light at the
opposite parallel faces AB (air-glass interface)
and CD (glass-air interface) of the rectangular
glass slab is equal and opposite. This is why
the ray emerges parallel to the incident ray.
However, the light ray is shifted sideward
slightly. What happens when a light ray is
incident normally to the interface of two
media? Try and find out.
Now you are familiar with the refraction of light. Refraction is due to
change in the speed of light as it enters from one transparent medium to
another. Experiments show that refraction of light occurs according to
certain laws.
Activity 9.10
Activity 9.10
Activity 9.10
Activity 9.10
Activity 9.10
n
Fix a sheet of white paper on a drawing board using drawing pins.
n
Place a rectangular glass slab over the sheet in the middle.
n
Draw the outline of the slab with a pencil. Let us name the outline
as ABCD.
n
Take four identical pins.
n
Fix two pins, say E and F, vertically such that the line joining the
pins is inclined to the edge AB.
n
Look for the images of the pins E and F through the opposite edge.
Fix two other pins, say G and H, such that these pins and the
images of E and F lie on a straight line.
n
Remove the pins and the slab.
n
Join the positions of tip of the pins E and F and produce the line
up to AB. Let EF meet AB at O. Similarly, join the positions of tip
of the pins G and H and produce it up to the edge CD. Let HG
meet CD at O′.
n
Join O and O′. Also produce EF up to P, as shown by a dotted line
in Fig. 9.10.
Figure 9.10
Figure 9.10
Figure 9.10
Figure 9.10
Figure 9.10
Refraction of light through a rectangular glass slab
2024-25 | Light – Reflection and Refraction 147 In this Activity, you will note, the light ray has changed its direction at points O and O′. Note that both the points O and O′ lie on surfaces separating two transparent media. Draw a perpendicular NN’ to AB at O and another perpendicular... |
Summarize the following historical passage: | Science
176
Figure 11.3
Figure 11.3
Figure 11.3
Figure 11.3
Figure 11.3
V–I graph for a nichrome wire. A
straight line plot shows that as the
current through a wire increases, the
potential difference across the wire
increases linearly – this is Ohm’s law.
Activity 11.2
Activity 11.2
Activity 11.2
Activity 11.2
Activity 11.2
n
Take a nichrome wire, a torch bulb, a 10 W bulb and an ammeter (0 – 5 A range), a plug
key and some connecting wires.
n
Set up the circuit by connecting four dry cells of 1.5 V each in series with the ammeter
leaving a gap XY in the circuit, as shown in Fig. 11.4.
In this Activity, you will find that approximately the
same value for V/I is obtained in each case. Thus the V–I
graph is a straight line that passes through the origin of
the graph, as shown in Fig. 11.3. Thus, V/I is a constant
ratio.
In 1827, a German physicist Georg Simon Ohm
(1787–1854) found out the relationship between the current
I, flowing in a metallic wire and the potential difference
across its terminals. The potential difference, V, across the
ends of a given metallic wire in an electric circuit is directly
proportional to the current flowing through it, provided its
temperature remains the same. This is called Ohm’s law. In
other words –
V ∝ I
(11.4)
or
V/I
=
constant
=
R
or
V
=
IR
(11.5)
In Eq. (11.4), R is a constant for the given metallic wire
at a given temperature and is called its resistance. It is the
property of a conductor to resist the flow of charges through it. Its SI
unit is ohm, represented by the Greek letter Ω. According to Ohm’s law,
R = V/I
(11.6)
If the potential difference across the two ends of a conductor is 1 V
and the current through it is 1 A, then the resistance R, of the conductor
is 1 Ω. That is, 1 ohm =
1 volt
1 ampere
Also from Eq. (11.5) we get
I = V/R
(11.7)
It is obvious from Eq. (11.7) that the current through a resistor is
inversely proportional to its resistance. If the resistance is doubled the
current gets halved. In many practical cases it is necessary to increase
or decrease the current in an electric circuit. A component used to
regulate current without changing the voltage source is called variable
resistance. In an electric circuit, a device called rheostat is often used to
change the resistance in the circuit. We will now study about electrical
resistance of a conductor with the help of following Activity.
2024-25 | Science 176 Figure 11.3 Figure 11.3 Figure 11.3 Figure 11.3 Figure 11.3 V–I graph for a nichrome wire. A straight line plot shows that as the current through a wire increases, the potential difference across the wire increases linearly – this is Ohm’s law. Activity 11.2 Activity 11.2 Activity 11.2... |
Summarize the following historical passage: | Life Processes
81
design in multi-cellular organisms are followed, a specialised tissue for
excretion will be developed, which means that the transportation system
will need to transport waste away from cells to this excretory tissue.
Let us consider these various processes, so essential to maintain
life, one by one.
Q
U
E
S
T
I
O
N
S
?
1.
Why is diffusion insufficient to meet the oxygen requirements of multi-
cellular organisms like humans?
2.
What criteria do we use to decide whether something is alive?
3.
What are outside raw materials used for by an organism?
4.
What processes would you consider essential for maintaining life?
5.2 NUTRITION
5.2 NUTRITION
5.2 NUTRITION
5.2 NUTRITION
5.2 NUTRITION
When we walk or ride a bicycle, we are using up energy. Even when we
are not doing any apparent activity, energy is needed to maintain a
state of order in our body. We also need materials from outside in order
to grow, develop, synthesise protein and other substances needed in
the body. This source of energy and materials is the food we eat.
How do living things get their food?
The general requirement for energy and materials is common in all
organisms, but it is fulfilled in different ways. Some organisms use simple
food material obtained from inorganic sources in the form of carbon
dioxide and water. These organisms, the autotrophs, include green
plants and some bacteria. Other organisms utilise complex substances.
These complex substances have to be broken down into simpler ones
before they can be used for the upkeep and growth of the body. To
achieve this, organisms use bio-catalysts called enzymes. Thus, the
heterotrophs survival depends directly or indirectly on autotrophs.
Heterotrophic organisms include animals and fungi.
5.2.1 Autotrophic Nutrition
Carbon and energy requirements of the autotrophic organism are
fulfilled by photosynthesis. It is the process by which autotrophs take
in substances from the outside and convert them into stored forms of
energy. This material is taken in the form of carbon dioxide and water
which is converted into carbohydrates in the presence of sunlight and
chlorophyll. Carbohydrates are utilised for providing energy to the plant.
We will study how this takes place in the next section. The carbohydrates
which are not used immediately are stored in the form of starch, which
serves as the internal energy reserve to be used as and when required
by the plant. A somewhat similar situation is seen in us where some of
the energy derived from the food we eat is stored in our body in the form
of glycogen.
2024-25 | Life Processes 81 design in multi-cellular organisms are followed, a specialised tissue for excretion will be developed, which means that the transportation system will need to transport waste away from cells to this excretory tissue. Let us consider these various processes, so essential to maintain life, one by one. Q... |
Summarize the following historical passage: | Science
4
Step I: To balance a chemical equation, first draw boxes around each
formula. Do not change anything inside the boxes while balancing the
equation.
Fe + H2O → Fe3O4 + H2
(1.5)
Step II: List the number of atoms of different elements present in the
unbalanced equation (1.5).
Element
Number of atoms
Number of atoms
in reactants (LHS)
in products (RHS)
Fe
1
3
H
2
2
O
1
4
To equalise the number of atoms, it must be remembered that we
cannot alter the formulae of the compounds or elements involved in the
reactions. For example, to balance oxygen atoms we can put coefficient
‘4’ as 4 H2O and not H2O4 or (H2O)4. Now the partly balanced equation
becomes –
Fe + 4 H2O → Fe3O4 + H2
Step IV: Fe and H atoms are still not balanced. Pick any of these elements
to proceed further. Let us balance hydrogen atoms in the partly balanced
equation.
To equalise the number of H atoms, make the number of molecules
of hydrogen as four on the RHS.
Step III: It is often convenient to start balancing with the compound
that contains the maximum number of atoms. It may be a reactant or a
product. In that compound, select the element which has the maximum
number of atoms. Using these criteria, we select Fe3O4 and the element
oxygen in it. There are four oxygen atoms on the RHS and only one on
the LHS.
To balance the oxygen atoms –
The equation would be –
Fe + 4 H2O → Fe3O4 + 4 H2
Atoms of
In reactants
In products
oxygen
(i)
Initial
1 (in H2O)
4 (in Fe3O4)
(ii)
To balance
1×4
4
Atoms of
In reactants
In products
hydrogen
(i)
Initial
8 (in 4 H2O)
2 (in H2)
(ii)
To balance
8
2 × 4
(1.6)
(partly balanced equation)
(1.7)
(partly balanced equation)
2024-25 | Science 4 Step I: To balance a chemical equation, first draw boxes around each formula. Do not change anything inside the boxes while balancing the equation. Fe + H2O → Fe3O4 + H2 (1.5) Step II: List the number of atoms of different elements present in the unbalanced equation (1.5).... |
Summarize the following historical passage: | Light – Reflection and Refraction
141
We consider two positions of the object for studying the image formed
by a convex mirror. First is when the object is at infinity and the second
position is when the object is at a finite distance from the mirror. The ray
diagrams for the formation of image by a convex mirror for these two
positions of the object are shown in Fig.9.8 (a) and (b), respectively. The
results are summarised in Table 9.2.
Activity 9.5
Activity 9.5
Activity 9.5
Activity 9.5
Activity 9.5
n
Take a convex mirror. Hold it in one hand.
n
Hold a pencil in the upright position in the other hand.
n
Observe the image of the pencil in the mirror. Is the image erect or
inverted? Is it diminished or enlarged?
n
Move the pencil away from the mirror slowly. Does the image
become smaller or larger?
n
Repeat this Activity carefully. State whether the image will move
closer to or farther away from the focus as the object is moved
away from the mirror?
Figure 9.8
Figure 9.8
Figure 9.8
Figure 9.8
Figure 9.8 Formation of image by a convex mirror
You have so far studied the image formation by a plane mirror, a
concave mirror and a convex mirror. Which of these mirrors will give the
full image of a large object? Let us explore through an Activity.
Activity 9.6
Activity 9.6
Activity 9.6
Activity 9.6
Activity 9.6
n
Observe the image of a distant object, say a distant tree, in a
plane mirror.
n
Could you see a full-length image?
Table 9.2 Nature, position and relative size of the image formed by a convex mirror
Position of the
Position of the
Size of the
Nature of the
object
image
image
image
At infinity
At the focus F,
Highly diminished,
Virtual and erect
behind the mirror
point-sized
Between infinity
Between P and F,
Diminished
Virtual and erect
and the pole P of
behind the mirror
the mirror
2024-25 | Light – Reflection and Refraction 141 We consider two positions of the object for studying the image formed by a convex mirror. First is when the object is at infinity and the second position is when the object is at a finite distance from the mirror. The ray diagrams for... |
Summarize the following historical passage: | Acids, Bases and Salts
33
Paris, the substance which doctors use as plaster for supporting
fractured bones in the right position. Plaster of Paris is a white powder
and on mixing with water, it changes to gypsum once again giving a
hard solid mass.
CaSO .1
2 H O +11
2 H O
CaSO .2H O
4
2
2
4
2
(Plaster of Paris)
Gypsum)
→
(
Note that only half a water molecule is shown to be attached as water
of crystallisation. How can you get half a water molecule? It is written in
this form because two formula units of CaSO4 share one molecule of
water. Plaster of Paris is used for making toys, materials for decoration
and for making surfaces smooth. Try to find out why is calcium sulphate
hemihydrate called ‘Plaster of Paris’ ?
1.
What is the common name of the compound CaOCl2?
2.
Name the substance which on treatment with chlorine yields bleaching
powder.
3.
Name the sodium compound which is used for softening hard water.
4.
What will happen if a solution of sodium hydrocarbonate is heated?
Give the equation of the reaction involved.
5.
Write an equation to show the reaction between Plaster of Paris and
water.
Q
U
E
S
T
I
O
N
S
?
What you have learnt
n
Acid-base indicators are dyes or mixtures of dyes which are used to indicate the
presence of acids and bases.
n
Acidic nature of a substance is due to the formation of H+(aq) ions in solution.
Formation of OH–(aq) ions in solution is responsible for the basic nature of a
substance.
n
When an acid reacts with a metal, hydrogen gas is evolved and a corresponding
salt is formed.
n
When a base reacts with a metal, along with the evolution of hydrogen gas a salt is
formed which has a negative ion composed of the metal and oxygen.
n
When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives
the corresponding salt, carbon dioxide gas and water.
n
Acidic and basic solutions in water conduct electricity because they produce
hydrogen and hydroxide ions respectively.
2024-25 | Acids, Bases and Salts 33 Paris, the substance which doctors use as plaster for supporting fractured bones in the right position. Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass. CaSO .1 2 H O +11... |
Summarize the following historical passage: | Science
154
(ii)
A ray of light passing
through a principal
focus, after refraction
from a convex lens, will
emerge parallel to the
principal axis. This is
shown in Fig. 9.14 (a). A
ray of light appearing to
meet at the principal
focus of a concave lens,
after refraction, will
emerge parallel to the
principal axis. This is
shown in Fig.9.14 (b).
(iii)
A ray of light passing
through the optical
centre of a lens will
emerge without any
deviation.
This
is
illustrated in Fig.9.15(a)
and Fig.9.15 (b).
(b)
(a)
(b)
(a)
The ray diagrams for the image formation in a convex lens for a few
positions of the object are shown in Fig. 9.16. The ray diagrams
representing the image formation in a concave lens for various positions
of the object are shown in Fig. 9.17.
Figure 9.14
Figure 9.14
Figure 9.14
Figure 9.14
Figure 9.14
Figure 9.15
Figure 9.15
Figure 9.15
Figure 9.15
Figure 9.15
2024-25 | Science 154 (ii) A ray of light passing through a principal focus, after refraction from a convex lens, will emerge parallel to the principal axis. This is shown in Fig. 9.14 (a). A ray of light appearing to meet at the principal focus of a concave lens, after refraction, will... |
Summarize the following historical passage: | Science
178
It is observed that the ammeter reading decreases to one-half when
the length of the wire is doubled. The ammeter reading is increased when
a thicker wire of the same material and of the same length is used in the
circuit. A change in ammeter reading is observed when a wire of different
material of the same length and the same area of cross-section is used.
On applying Ohm’s law [Eqs. (11.5) – (11.7)], we observe that the
resistance of the conductor depends (i) on its length, (ii) on its area of
cross-section, and (iii) on the nature of its material. Precise measurements
have shown that resistance of a uniform metallic conductor is directly
proportional to its length (l) and inversely proportional to the area of
cross-section (A). That is,
R ∝ l
(11.8)
and
R ∝ 1/A
(11.9)
Combining Eqs. (11.8) and (11.9) we get
R ∝ l
A
or,
R = ρ l
A
(11.10)
where ρ (rho) is a constant of proportionality and is called the electrical
resistivity of the material of the conductor. The SI unit of resistivity is
Ω m. It is a characteristic property of the material. The metals and alloys
Figure 11.5
Figure 11.5
Figure 11.5
Figure 11.5
Figure 11.5 Electric circuit to study the factors on which the resistance of conducting wires depends
n
Now, plug the key. Note the current in the ammeter.
n
Replace the nichrome wire by another nichrome wire of same thickness but twice the
length, that is 2l [marked (2) in the Fig. 11.5].
n
Note the ammeter reading.
n
Now replace the wire by a thicker nichrome wire, of the same length l [marked (3)]. A
thicker wire has a larger cross-sectional area. Again note down the current through the
circuit.
n
Instead of taking a nichrome wire, connect a copper wire [marked (4) in Fig. 11.5] in the
circuit. Let the wire be of the same length and same area of cross-section as that of the
first nichrome wire [marked (1)]. Note the value of the current.
n
Notice the difference in the current in all cases.
n
Does the current depend on the length of the conductor?
n
Does the current depend on the area of cross-section of the wire used?
2024-25 | Science 178 It is observed that the ammeter reading decreases to one-half when the length of the wire is doubled. The ammeter reading is increased when a thicker wire of the same material and of the same length is used in the circuit. A change in ammeter reading is observed... |
Summarize the following historical passage: | Science
102
6.1.1 What happens in Reflex Actions?
‘Reflex’ is a word we use very commonly when we talk about some sudden
action in response to something in the environment. We say ‘I jumped
out of the way of the bus reflexly’, or ‘I pulled my hand back from the
flame reflexly’, or ‘I was so hungry my mouth started watering reflexly’.
What exactly do we mean? A common idea in all such examples is that
we do something without thinking about it, or without feeling in control
of our reactions. Yet these are situations where we are responding with
some action to changes in our environment. How is control and
coordination achieved in such situations?
Let us consider this further. Take one of our examples. Touching a
flame is an urgent and dangerous situation for us, or in fact, for any
animal! How would we respond to this? One seemingly simple way is to
think consciously about the pain and the possibility of getting burnt,
and therefore move our hand. An important question then is, how long
will it take us to think all this? The answer depends on how we think. If
nerve impulses are sent around the way we have talked about earlier,
then thinking is also likely to involve the creation of such impulses.
Thinking is a complex activity, so it is bound to involve a complicated
interaction of many nerve impulses from many neurons.
If this is the case, it is no surprise that the thinking tissue in our
body consists of dense networks of intricately arranged neurons. It sits
in the forward end of the skull, and receives signals from all over the
body which it thinks about before responding to them. Obviously, in
order to receive these signals, this thinking part of the brain in the skull
must be connected to nerves coming from various parts of the body.
Similarly, if this part of the brain is to instruct muscles to move, nerves
must carry this signal back to different parts of the body. If all of this is
to be done when we touch a hot object, it may take enough time for us to
get burnt!
How does the design of the body solve this problem? Rather than
having to think about the sensation of heat, if the nerves that detect heat
were to be connected to the nerves that move muscles in a simpler way,
the process of detecting the signal or the input and responding to it by
an output action might be completed quickly. Such a connection is
commonly called a reflex arc (Fig. 6.2). Where should such reflex arc
connections be made between the input nerve and the output nerve?
The best place, of course, would be at the point where they first meet
each other. Nerves from all over the body meet in a bundle in the spinal
cord on their way to the brain. Reflex arcs are formed in this spinal cord
itself, although the information input also goes on to reach the brain.
Of course, reflex arcs have evolved in animals because the thinking
process of the brain is not fast enough. In fact many animals have very
little or none of the complex neuron network needed for thinking. So it is
quite likely that reflex arcs have evolved as efficient ways of functioning
in the absence of true thought processes. However, even after complex
neuron networks have come into existence, reflex arcs continue to be
more efficient for quick responses.
2024-25 | Science 102 6.1.1 What happens in Reflex Actions? ‘Reflex’ is a word we use very commonly when we talk about some sudden action in response to something in the environment. We say ‘I jumped out of the way of the bus reflexly’, or ‘I pulled my hand back from the... |
Summarize the following historical passage: | Science
208
Activity 13.1
Activity 13.1
Activity 13.1
Activity 13.1
Activity 13.1
Our Environment
13
CHAPTER
W
e have heard the word ‘environment’ often being used on the
television, in newspapers and by people around us. Our elders tell
us that the ‘environment’ is not what it used to be earlier; others say that
we should work in a healthy ‘environment’; and global summits involving
the developed and developing countries are regularly held to discuss
‘environmental’ issues. In this chapter, we shall be studying how various
components in the environment interact with each other and how we
impact the environment.
13.1 ECO
13.1 ECO
13.1 ECO
13.1 ECO
13.1 ECO-SYSTEM — WHA
-SYSTEM — WHA
-SYSTEM — WHA
-SYSTEM — WHA
-SYSTEM — WHAT ARE ITS COMPONENTS?
T ARE ITS COMPONENTS?
T ARE ITS COMPONENTS?
T ARE ITS COMPONENTS?
T ARE ITS COMPONENTS?
All organisms such as plants, animals, microorganisms and human
beings as well as the physical surroundings interact with each other
and maintain a balance in nature. All the interacting organisms in an
area together with the non-living constituents of the environment form
an ecosystem. Thus, an ecosystem consists of biotic components
comprising living organisms and abiotic components comprising
physical factors like temperature, rainfall, wind, soil and minerals.
For example, if you visit a garden you will find different plants, such
as grasses, trees; flower bearing plants like rose, jasmine, sunflower;
and animals like frogs, insects and birds. All these living organisms
interact with each other and their growth, reproduction and other
activities are affected by the abiotic components of ecosystem. So a garden
is an ecosystem. Other types of ecosystems are forests, ponds and lakes.
These are natural ecosystems while gardens and crop-fields are human-
made (artificial) ecosystems.
n
You might have seen an aquarium. Let us try to design one.
n
What are the things that we need to keep in mind when we create
an aquarium? The fish would need a free space for swimming (it
could be a large jar), water, oxygen and food.
n
We can provide oxygen through an oxygen pump (aerator) and
fish food which is available in the market.
2024-25 | Science 208 Activity 13.1 Activity 13.1 Activity 13.1 Activity 13.1 Activity 13.1 Our Environment 13 CHAPTER W e have heard the word ‘environment’ often being used on the television, in newspapers and by people around us. Our elders tell us that the ‘environment’ is not what it used to be... |
Summarize the following historical passage: | Science
96
energy. Material like sucrose is transferred into phloem tissue using
energy from ATP. This increases the osmotic pressure of the tissue
causing water to move into it. This pressure moves the material in the
phloem to tissues which have less pressure. This allows the phloem to
move material according to the plant’s needs. For example, in the spring,
sugar stored in root or stem tissue would be transported to the buds
which need energy to grow.
Q
U
E
S
T
I
O
N
S
?
1.
What are the components of the transport system in human beings?
What are the functions of these components?
2.
Why is it necessary to separate oxygenated and deoxygenated blood in
mammals and birds?
3.
What are the components of the transport system in highly organised
plants?
4.
How are water and minerals transported in plants?
5.
How is food transported in plants?
5.5 EX
5.5 EX
5.5 EX
5.5 EX
5.5 EXCRETION
CRETION
CRETION
CRETION
CRETION
We have already discussed how organisms get rid of gaseous wastes
generated during photosynthesis or respiration. Other metabolic activities
generate nitrogenous materials which need to be removed. The biological
process involved in the removal of these harmful metabolic wastes from
the body is called excretion. Different organisms use varied strategies to
do this. Many unicellular organisms remove these wastes by simple
diffusion from the body surface into the surrounding
water. As we have seen in other processes, complex
multi-cellular organisms use specialised organs to
perform the same function.
5.5.1 Excretion in Human Beings
The excretory system of human beings (Fig. 5.13)
includes a pair of kidneys, a pair of ureters, a urinary
bladder and a urethra. Kidneys are located in the
abdomen, one on either side of the backbone. Urine
produced in the kidneys passes through the ureters
into the urinary bladder where it is stored until it is
released through the urethra.
How is urine produced? The purpose of making
urine is to filter out waste products from the blood.
Just as CO2 is removed from the blood in the lungs,
nitrogenous waste such as urea or uric acid are
removed from blood in the kidneys. It is then no
surprise that the basic filtration unit in the kidneys,
Figure 5.13
Excretory system in human beings
2024-25 | Science 96 energy. Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material... |
Summarize the following historical passage: | Science
128
Figure 8.1
Figure 8.1
Figure 8.1
Figure 8.1
Figure 8.1
Creation of diversity over succeeding
generations. The original organism at the top
will give rise to, say, two individuals, similar
in body design, but with subtle differences.
Each of them, in turn, will give rise to two
individuals in the next generation. Each of
the four individuals in the bottom row will
be different from each other. While some of
these differences will be unique, others will
be inherited from their respective parents,
who were different from each other.
Heredity
8
CHAPTER
W
e have seen that reproductive processes give rise to new individuals
that are similar, but subtly different. We have discussed how some
amount of variation is produced even during asexual reproduction. And
the number of successful variations are maximised by the process of
sexual reproduction. If we observe a field of sugarcane we find very little
variations among the individual plants. But in a number of animals
including human beings, which reproduce sexually, quite distinct
variations are visible among different individuals. In this chapter, we
shall be studying the mechanism by which variations are created and
inherited.
8.1
8.1
8.1
8.1
8.1 AAAAACCUMUL
CCUMUL
CCUMUL
CCUMUL
CCUMULAAAAATION OF V
TION OF V
TION OF V
TION OF V
TION OF VARIA
ARIA
ARIA
ARIA
ARIATION
TION
TION
TION
TION
DURING REPRODUCTION
DURING REPRODUCTION
DURING REPRODUCTION
DURING REPRODUCTION
DURING REPRODUCTION
Inheritance from the previous generation provides
both a common basic body design, and subtle
changes in it, for the next generation. Now think
about what would happen when this new generation,
in its turn, reproduces. The second generation will
have differences that they inherit from the first
generation, as well as newly created differences
(Fig. 8.1).
Figure 8.1 would represent the situation if a
single individual reproduces, as happens in asexual
reproduction. If one bacterium divides, and then the
resultant two bacteria divide again, the four
individual bacteria generated would be very similar.
There would be only very minor differences between
them, generated due to small inaccuracies in DNA
copying. However, if sexual reproduction is involved,
even greater diversity will be generated, as we will
see when we discuss the rules of inheritance.
Do all these variations in a species have equal
chances of surviving in the environment in which they
find themselves? Obviously not. Depending on the
nature of variations, different individuals would have
2024-25 | Science 128 Figure 8.1 Figure 8.1 Figure 8.1 Figure 8.1 Figure 8.1 Creation of diversity over succeeding generations. The original organism at the top will give rise to, say, two individuals, similar in body design, but with subtle differences. Each of them, in turn, will give rise to two individuals... |
Summarize the following historical passage: | Control and Coordination
109
6.3 HORMONES IN ANIMALS
6.3 HORMONES IN ANIMALS
6.3 HORMONES IN ANIMALS
6.3 HORMONES IN ANIMALS
6.3 HORMONES IN ANIMALS
How are such chemical, or hormonal, means of information transmission
used in animals? What do some animals, for instance squirrels,
experience when they are in a scary situation? Their bodies have to
prepare for either fighting or running away. Both are very complicated
activities that will use a great deal of energy in controlled ways. Many
different tissue types will be used and their activities integrated together
in these actions. However, the two alternate activities, fighting or running,
are also quite different! So here is a situation in which some common
preparations can be usefully made in the body. These preparations
should ideally make it easier to do either activity in the near future. How
would this be achieved?
If the body design in the squirrel relied only on electrical impulses
via nerve cells, the range of tissues instructed to prepare for the coming
activity would be limited. On the other hand, if a chemical signal were to
be sent as well, it would reach all cells of the body and provide the wide-
ranging changes needed. This is done in many animals, including human
beings, using a hormone called adrenaline that is secreted from the
adrenal glands. Look at Fig. 6.7 to locate these glands.
Adrenaline is secreted directly into the blood and carried to different
parts of the body. The target organs or the specific tissues on which it
acts include the heart. As a result, the heart beats faster, resulting in
supply of more oxygen to our muscles. The blood to the digestive system
and skin is reduced due to contraction of muscles around small arteries
in these organs. This diverts the blood to our skeletal muscles. The
breathing rate also increases because of the contractions of the
diaphragm and the rib muscles. All these responses together enable the
animal body to be ready to deal with the situation. Such animal hormones
are part of the endocrine system which constitutes a second way of control
and coordination in our body.
Activity 6.3
Activity 6.3
Activity 6.3
Activity 6.3
Activity 6.3
n
Look at Fig. 6.7.
n
Identify the endocrine glands mentioned in the figure.
n
Some of these glands have been listed in Table 6.1 and discussed
in the text. Consult books in the library and discuss with your
teachers to find out about other glands.
Remember that plants have hormones that control their directional
growth. What functions do animal hormones perform? On the face of it,
we cannot imagine their role in directional growth. We have never seen
an animal growing more in one direction or the other, depending on
light or gravity! But if we think about it a bit more, it will become evident
that, even in animal bodies, growth happens in carefully controlled places.
Plants will grow leaves in many places on the plant body, for example.
But we do not grow fingers on our faces. The design of the body is carefully
maintained even during the growth of children.
2024-25 | Control and Coordination 109 6.3 HORMONES IN ANIMALS 6.3 HORMONES IN ANIMALS 6.3 HORMONES IN ANIMALS 6.3 HORMONES IN ANIMALS 6.3 HORMONES IN ANIMALS How are such chemical, or hormonal, means of information transmission used in animals? What do some animals, for instance squirrels, experience when they are in a... |
Summarize the following historical passage: | Science
112
E
X
E
R
C
I
S
E
S
1. Which of the following is a plant hormone?
(a)
Insulin
(b)
Thyroxin
(c)
Oestrogen
(d)
Cytokinin.
2. The gap between two neurons is called a
(a)
dendrite.
(b)
synapse.
(c)
axon.
(d)
impulse.
3. The brain is responsible for
(a)
thinking.
(b)
regulating the heart beat.
(c)
balancing the body.
(d)
all of the above.
4. What is the function of receptors in our body? Think of situations where receptors
do not work properly. What problems are likely to arise?
5. Draw the structure of a neuron and explain its function.
6. How does phototropism occur in plants?
7. Which signals will get disrupted in case of a spinal cord injury?
8. How does chemical coordination occur in plants?
9. What is the need for a system of control and coordination in an organism?
10. How are involuntary actions and reflex actions different from each other?
11. Compare and contrast nervous and hormonal mechanisms for control and
coordination in animals.
12. What is the difference between the manner in which movement takes place in a
sensitive plant and the movement in our legs?
2024-25 | Science 112 E X E R C I S E S 1. Which of the following is a plant hormone? (a) Insulin (b) Thyroxin (c) Oestrogen (d) Cytokinin. 2. The gap between two neurons is called a (a) dendrite. (b) synapse. (c) axon. (d) impulse. 3. The brain is responsible... |
Summarize the following historical passage: | Electricity
193
E
X
E
R
C
I
S
E
S
1.
A piece of wire of resistance R is cut into five equal parts. These parts are then
connected in parallel. If the equivalent resistance of this combination is R′, then the
ratio R/R′ is –
(a) 1/25
(b) 1/5
(c) 5
(d) 25
2.
Which of the following terms does not represent electrical power in a circuit?
(a) I2R
(b) IR2
(c) VI
(d) V2/R
3.
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the
power consumed will be –
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W
4.
Two conducting wires of the same material and of equal lengths and equal diameters
are first connected in series and then parallel in a circuit across the same potential
difference. The ratio of heat produced in series and parallel combinations would be –
(a) 1:2
(b) 2:1
(c) 1:4
(d) 4:1
5.
How is a voltmeter connected in the circuit to measure the potential difference between
two points?
6.
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10–8 Ω m. What will be
the length of this wire to make its resistance 10 Ω? How much does the resistance
change if the diameter is doubled?
7.
The values of current I flowing in a given resistor for the corresponding values of
potential difference V across the resistor are given below –
I (amperes)
0.5
1.0
2.0
3.0
4.0
V (volts)
1.6
3.4
6.7
10.2
13.2
Plot a graph between V and I and calculate the resistance of that resistor.
8.
When a 12 V battery is connected across an unknown resistor, there is a current
of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
9.
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω , 0.5 Ω
and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
10. How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
11. Show how you would connect three resistors, each of resistance 6 Ω, so that the
combination has a resistance of (i) 9 Ω, (ii) 4 Ω.
12. Several electric bulbs designed to be used on a 220 V electric supply line, are
rated 10 W. How many lamps can be connected in parallel with each other across
the two wires of 220 V line if the maximum allowable current is 5 A?
13. A hot plate of an electric oven connected to a 220 V line has two resistance coils
A and B, each of 24 Ω resistance, which may be used separately, in series, or in
parallel. What are the currents in the three cases?
14. Compare the power used in the 2 Ω resistor in each of the following circuits:
(i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel
with 12 Ω and 2 Ω resistors.
2024-25 | Electricity 193 E X E R C I S E S 1. A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R′, then the ratio R/R′ is – (a) 1/25 (b)... |
Summarize the following historical passage: | Electricity
181
Q
U
E
S
T
I
O
N
S
?
1.
On what factors does the resistance of a
conductor depend?
2.
Will current flow more easily through a thick
wire or a thin wire of the same material, when
connected to the same source? Why?
3.
Let the resistance of an electrical component
remains constant while the potential difference
across the two ends of the component
decreases to half of its former value. What
change will occur in the current through it?
4.
Why are coils of electric toasters and electric
irons made of an alloy rather than a pure
metal?
5.
Use the data in Table 11.2 to answer the
following –
(a) Which among iron and mercury is a better
conductor?
(b) Which material is the best conductor?
11.6 RESIST
11.6 RESIST
11.6 RESIST
11.6 RESIST
11.6 RESISTANCE OF A SYSTEM OF RESISTORS
ANCE OF A SYSTEM OF RESISTORS
ANCE OF A SYSTEM OF RESISTORS
ANCE OF A SYSTEM OF RESISTORS
ANCE OF A SYSTEM OF RESISTORS
In preceding sections, we learnt about some simple electric circuits. We
have noticed how the current through a conductor depends upon its
resistance and the potential difference across its ends. In various electrical
gadgets, we often use resistors in various combinations. We now therefore
intend to see how Ohm’s law can be applied to combinations of resistors.
There are two methods of joining the resistors together. Figure 11.6
shows an electric circuit in which three resistors having resistances R1,
R2 and R3, respectively, are joined end to end. Here the resistors are said
to be connected in series.
Figure 11.6
Figure 11.6
Figure 11.6
Figure 11.6
Figure 11.6 Resistors in series
2024-25 | Electricity 181 Q U E S T I O N S ? 1. On what factors does the resistance of a conductor depend? 2. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why? 3. Let... |
Summarize the following historical passage: | Light – Reflection and Refraction
135
Let us recall these laws –
(i)
The angle of incidence is equal to the angle of reflection, and
(ii)
The incident ray, the normal to the mirror at the point of incidence
and the reflected ray, all lie in the same plane.
These laws of reflection are applicable to all types of reflecting surfaces
including spherical surfaces. You are familiar with the formation of image
by a plane mirror. What are the properties of the image? Image formed
by a plane mirror is always virtual and erect. The size of the image is
equal to that of the object. The image formed is as far behind the mirror
as the object is in front of it. Further, the image is laterally inverted.
How would the images be when the reflecting surfaces are curved? Let
us explore.
Activity 9.1
Activity 9.1
Activity 9.1
Activity 9.1
Activity 9.1
n
Take a large shining spoon. Try to view your face in its curved
surface.
n
Do you get the image? Is it smaller or larger?
n
Move the spoon slowly away from your face. Observe the image.
How does it change?
n
Reverse the spoon and repeat the Activity. How does the image
look like now?
n
Compare the characteristics of the image on the two surfaces.
The curved surface of a shining spoon could be considered as a curved
mirror. The most commonly used type of curved mirror is the spherical
mirror. The reflecting surface of such mirrors can be considered to form
a part of the surface of a sphere. Such mirrors, whose reflecting surfaces
are spherical, are called spherical mirrors. We shall now study about
spherical mirrors in some detail.
9.2 SPHERIC
9.2 SPHERIC
9.2 SPHERIC
9.2 SPHERIC
9.2 SPHERICAL MIRRORS
AL MIRRORS
AL MIRRORS
AL MIRRORS
AL MIRRORS
The reflecting surface of a spherical mirror may be curved inwards or
outwards. A spherical mirror, whose reflecting surface is curved inwards,
that is, faces towards the centre of the sphere, is called a concave mirror.
A spherical mirror whose reflecting surface is curved outwards, is called
a convex mirror. The schematic representation of these mirrors is shown
in Fig. 9.1. You may note in these diagrams that the back
of the mirror is shaded.
You may now understand that the surface of the spoon
curved inwards can be approximated to a concave mirror
and the surface of the spoon bulged outwards can be
approximated to a convex mirror.
Before we move further on spherical mirrors, we need to
recognise and understand the meaning of a few terms. These
terms are commonly used in discussions about spherical
mirrors. The centre of the reflecting surface of a spherical
mirror is a point called the pole. It lies on the surface of the
mirror. The pole is usually represented by the letter P.
Figure 9.1
Figure 9.1
Figure 9.1
Figure 9.1
Figure 9.1
Schematic representation of spherical
mirrors; the shaded side is non-reflecting.
(a) Concave mirror
(b) Convex mirror
2024-25 | Light – Reflection and Refraction 135 Let us recall these laws – (i) The angle of incidence is equal to the angle of reflection, and (ii) The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane. These... |
Summarize the following historical passage: | Metals and Non-metals
45
n
In which test tube did you find that a reaction has occurred?
n
On what basis can you say that a reaction has actually taken
place?
n
Can you correlate your observations for the Activities 3.9, 3.10
and 3.11?
n
Write a balanced chemical equation for the reaction that has taken
place.
n
Name the type of reaction.
Reactive metals can displace less
reactive metals from their compounds in
solution or molten form.
We have seen in the previous sections
that all metals are not equally reactive. We
checked the reactivity of various metals
with oxygen, water and acids. But all
metals do not react with these reagents.
So we were not able to put all the metal
samples we had collected in decreasing
order of their reactivity. Displacement
reactions studied in Chapter 1 give better
evidence about the reactivity of metals. It
is simple and easy if metal A displaces
metal B from its solution, it is more reactive than B.
Metal A + Salt solution of B → Salt solution of A + Metal B
Which metal, copper or iron, is more reactive according to your
observations in Activity 3.12?
3.2.5 The Reactivity Series
The reactivity series is a list of metals arranged in the order of their
decreasing activities. After performing displacement experiments
(Activities 1.9 and 3.12), the following series, (Table 3.2) known as the
reactivity or activity series has been developed.
Table 3.2 Activity series : Relative reactivities of metals
K
Potassium
Most reactive
Na
Sodium
Ca
Calcium
Mg
Magnesium
Al
Aluminium
Zn
Zinc
Reactivity decreases
Fe
Iron
Pb
Lead
[H]
[Hydrogen]
Cu
Copper
Hg
Mercury
Ag
Silver
Au
Gold
Least reactive
Figure 3.4
Figure 3.4
Figure 3.4
Figure 3.4
Figure 3.4
Reaction of metals with
salt solutions
2024-25 | Metals and Non-metals 45 n In which test tube did you find that a reaction has occurred? n On what basis can you say that a reaction has actually taken place? n Can you correlate your observations for the Activities 3.9, 3.10 and 3.11? n Write a balanced chemical equation... |
Summarize the following historical passage: | How do Organisms Reproduce?
127
E
X
E
R
C
I
S
E
S
1.
Asexual reproduction takes place through budding in
(a)
Amoeba.
(b)
Yeast.
(c)
Plasmodium.
(d)
Leishmania.
2.
Which of the following is not a part of the female reproductive system in human
beings?
(a)
Ovary
(b)
Uterus
(c)
Vas deferens
(d)
Fallopian tube
3.
The anther contains
(a)
sepals.
(b)
ovules.
(c)
pistil.
(d)
pollen grains.
4.
What are the advantages of sexual reproduction over asexual reproduction?
5.
What are the functions performed by the testis in human beings?
6.
Why does menstruation occur?
7.
Draw a labelled diagram of the longitudinal section of a flower.
8.
What are the different methods of contraception?
9.
How are the modes for reproduction different in unicellular and
multicellular organisms?
10. How does reproduction help in providing stability to populations of species?
11. What could be the reasons for adopting contraceptive methods?
2024-25 | How do Organisms Reproduce? 127 E X E R C I S E S 1. Asexual reproduction takes place through budding in (a) Amoeba. (b) Yeast. (c) Plasmodium. (d) Leishmania. 2. Which of the following is not a part of the female reproductive system in human beings? (a) Ovary (b)... |
Summarize the following historical passage: | Acids, Bases and Salts
19
Which of these – vanilla, onion and clove, can be used as olfactory
indicators on the basis of your observations?
Let us do some more activities to understand the chemical properties
of acids and bases.
2.1.2 How do Acids and Bases React with Metals?
n
Rinse both cloth strips with water and again check their odour.
n
Note your observations.
n
Now take some dilute vanilla essence and clove oil and check their
odour.
n
Take some dilute HCl solution in one test tube and dilute NaOH
solution in another. Add a few drops of dilute vanilla essence to
both test tubes and shake well. Check the odour once again and
record changes in odour, if any.
n
Similarly, test the change in the odour of clove oil with dilute HCl
and dilute NaOH solutions and record your observations.
Activity 2.3
Activity 2.3
Activity 2.3
Activity 2.3
Activity 2.3
CAUTION: This activity needs the teacher’s assistance.
n Set the apparatus as shown in Fig. 2.1.
n Take about 5 mL of dilute sulphuric acid in a test tube and add a
few pieces of zinc granules to it.
n What do you observe on the surface of zinc granules?
n Pass the gas being evolved through the soap solution.
n Why are bubbles formed in the soap solution?
n Take a burning candle near a gas filled bubble.
n What do you observe?
n Repeat this Activity with some more acids like HCl, HNO3 and
CH3COOH.
n Are the observations in all the cases the same or different?
Figure 2.1
Figure 2.1
Figure 2.1
Figure 2.1
Figure 2.1 Reaction of zinc granules with dilute sulphuric acid and testing hydrogen
gas by burning
2024-25 | Acids, Bases and Salts 19 Which of these – vanilla, onion and clove, can be used as olfactory indicators on the basis of your observations? Let us do some more activities to understand the chemical properties of acids and bases. 2.1.2 How do Acids and Bases React with Metals? n... |
Summarize the following historical passage: | Electricity
11
CHAPTER
E
lectricity has an important place in modern society. It is a controllable
and convenient form of energy for a variety of uses in homes, schools,
hospitals, industries and so on. What constitutes electricity? How does
it flow in an electric circuit? What are the factors that control or regulate
the current through an electric circuit? In this Chapter, we shall attempt
to answer such questions. We shall also discuss the heating effect of
electric current and its applications.
11.1 ELECTRIC CURRENT AND CIRCUIT
11.1 ELECTRIC CURRENT AND CIRCUIT
11.1 ELECTRIC CURRENT AND CIRCUIT
11.1 ELECTRIC CURRENT AND CIRCUIT
11.1 ELECTRIC CURRENT AND CIRCUIT
We are familiar with air current and water current. We know that flowing
water constitute water current in rivers. Similarly, if the electric charge
flows through a conductor (for example, through a metallic wire), we
say that there is an electric current in the conductor. In a torch, we
know that the cells (or a battery, when placed in proper order) provide
flow of charges or an electric current through the torch bulb to glow. We
have also seen that the torch gives light only when its switch is on. What
does a switch do? A switch makes a conducting link between the cell and
the bulb. A continuous and closed path of an electric current is called an
electric circuit. Now, if the circuit is broken anywhere (or the switch of the
torch is turned off ), the current stops flowing and the bulb does not glow.
How do we express electric current? Electric current is expressed by
the amount of charge flowing through a particular area in unit time. In
other words, it is the rate of flow of electric charges. In circuits using
metallic wires, electrons constitute the flow of charges. However, electrons
were not known at the time when the phenomenon of electricity was first
observed. So, electric current was considered to be the flow of positive
charges and the direction of flow of positive charges was taken to be the
direction of electric current. Conventionally, in an electric circuit the
direction of electric current is taken as opposite to the direction of the
flow of electrons, which are negative charges.
2024-25 | Electricity 11 CHAPTER E lectricity has an important place in modern society. It is a controllable and convenient form of energy for a variety of uses in homes, schools, hospitals, industries and so on. What constitutes electricity? How does it flow in an electric circuit? What are the factors that... |
Summarize the following historical passage: | Light – Reflection and Refraction
157
Solution
Height of the object h
= + 2.0 cm;
Focal length f
= + 10 cm;
object-distance u
= –15 cm;
Image-distance v
= ?
Height of the image h′ = ?
Since
1
1
1
v
u
f
−
=
or,
1
1
1
v
u
f
=
+
1
1
1
1
1
( 15)
10
15
10
v =
+
= −
+
−
1
2
3
1
30
30
v
−
+
=
=
or,
v = + 30 cm
The positive sign of v shows that the image is formed at a distance of
30 cm on the other side of the optical centre. The image is real and
inverted.
Magnification m =
'
h
v
h
u
=
or,
h′ = h (v/u)
Height of the image, h′ = (2.0) (+30/–15) = – 4.0 cm
Magnification m = v/u
or,
30cm
2
15cm
m
+
=
= −
−
The negative signs of m and h′ show that the image is inverted and
real. It is formed below the principal axis. Thus, a real, inverted image,
4 cm tall, is formed at a distance of 30 cm on the other side of the
lens. The image is two times enlarged.
9.3.8 Power of a Lens
You have already learnt that the ability of a lens to converge or diverge
light rays depends on its focal length. For example, a convex lens of
short focal length bends the light rays through large angles, by focussing
them closer to the optical centre. Similarly, concave lens of very short
focal length causes higher divergence than the one with longer focal
length. The degree of convergence or divergence of light rays achieved
by a lens is expressed in terms of its power. The power of a lens is defined
as the reciprocal of its focal length. It is represented by the letter P. The
power P of a lens of focal length f is given by
P =
1
f
(9.11)
2024-25 | Light – Reflection and Refraction 157 Solution Height of the object h = + 2.0 cm; Focal length f = + 10 cm; object-distance u = –15 cm; Image-distance v = ? Height of the image h′ = ? Since 1 1 1 v u f − = or, 1... |
Summarize the following historical passage: | Science
174
W
=
VQ
=
12 V × 2 C
=
24 J.
Q
U
E
S
T
I
O
N
S
?
11.3 CIRCUIT DIAGRAM
11.3 CIRCUIT DIAGRAM
11.3 CIRCUIT DIAGRAM
11.3 CIRCUIT DIAGRAM
11.3 CIRCUIT DIAGRAM
We know that an electric circuit, as shown in Fig. 11.1, comprises a cell
(or a battery), a plug key, electrical component(s), and connecting wires.
It is often convenient to draw a schematic diagram, in which different
components of the circuit are represented by the symbols conveniently
used. Conventional symbols used to represent some of the most
commonly used electrical components are given in Table 11.1.
Table 11.1 Symbols of some commonly used components in circuit diagrams
Sl.
Components
Symbols
No.
1
An electric cell
2
A battery or a combination of cells
3
Plug key or switch (open)
4
Plug key or switch (closed)
5
A wire joint
6
Wires crossing without joining
1.
Name a device that helps to maintain a potential difference across a
conductor.
2.
What is meant by saying that the potential difference between two points
is 1 V?
3.
How much energy is given to each coulomb of charge passing through a
6 V battery?
2024-25 | Science 174 W = VQ = 12 V × 2 C = 24 J. Q U E S T I O N S ? 11.3 CIRCUIT DIAGRAM 11.3 CIRCUIT DIAGRAM 11.3 CIRCUIT DIAGRAM 11.3 CIRCUIT DIAGRAM 11.3 CIRCUIT DIAGRAM We know that an electric circuit, as shown in Fig. 11.1,... |
Summarize the following historical passage: | Acids, Bases and Salts
21
Activity 2.6
Activity 2.6
Activity 2.6
Activity 2.6
Activity 2.6
n
Take about 2 mL of dilute NaOH solution in a test tube and add
two drops of phenolphthalein solution.
n
What is the colour of the solution?
n
Add dilute HCl solution to the above solution drop by drop.
n
Is there any colour change for the reaction mixture?
n
Why did the colour of phenolphthalein change after the addition
of an acid?
n
Now add a few drops of NaOH to the above mixture.
n
Does the pink colour of phenolphthalein reappear?
n
Why do you think this has happened?
On passing excess carbon dioxide the following reaction takes place:
CaCO s
Ca(HCO
aq
3
3
( )
) (
)
+
→
H O(l)+ CO (g)
2
2
2
(Soluble in water)
Limestone, chalk and marble are different forms of calcium carbonate.
All metal carbonates and hydrogencarbonates react with acids to give a
corresponding salt, carbon dioxide and water.
Thus, the reaction can be summarised as –
In the above Activity, we have observed that the effect of a base is
nullified by an acid and vice-versa. The reaction taking place is written as –
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
The reaction between an acid and a base to give a salt and water is
known as a neutralisation reaction. In general, a neutralisation reaction
can be written as –
Base + Acid → Salt + Water
2.1.5 Reaction of Metallic Oxides with Acids
Activity 2.7
Activity 2.7
Activity 2.7
Activity 2.7
Activity 2.7
n
Take a small amount of copper oxide in a beaker and add dilute
hydrochloric acid slowly while stirring.
n
Note the colour of the solution. What has happened to the copper
oxide?
You will notice that the colour of the solution becomes blue-green
and the copper oxide dissolves. The blue-green colour of the solution is
due to the formation of copper(II) chloride in the reaction. The general
reaction between a metal oxide and an acid can be written as –
Metal oxide + Acid → Salt + Water
Metal carbonate/Metal hydrogencarbonate + Acid → Salt + Carbon dioxide + Water
2.1.4 How do Acids and Bases React with each other?
2024-25 | Acids, Bases and Salts 21 Activity 2.6 Activity 2.6 Activity 2.6 Activity 2.6 Activity 2.6 n Take about 2 mL of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution. n What is the colour of the solution? n Add dilute HCl solution to the... |
Summarize the following historical passage: | Science
104
all this, a decision is made about how to respond and the information is
passed on to the motor areas which control the movement of voluntary
muscles, for example, our leg muscles. However, certain sensations are
distinct from seeing or hearing, for example, how do we know that we
have eaten enough? The sensation of feeling full is because of a centre
associated with hunger, which is in a separate part of the fore-brain.
Study the labelled diagram of the human brain. We have seen that
the different parts have specific functions. Can we find out the function
of each part?
Let us look at the other use of the word ‘reflex’ that we have talked
about in the introduction. Our mouth waters when we see food we like
without our meaning to. Our hearts beat without our thinking about it.
In fact, we cannot control these actions easily by thinking about them
even if we wanted to. Do we have to think about or remember to breathe
or digest food? So, in between the simple reflex actions like change in
the size of the pupil, and the thought out actions such as moving a
chair, there is another set of muscle movements over which we do not
have any thinking control. Many of these involuntary actions are
controlled by the mid-brain and hind-brain. All these involuntary actions
including blood pressure, salivation and vomiting are controlled by the
medulla in the hind-brain.
Think about activities like walking in a straight line, riding a bicycle,
picking up a pencil. These are possible due to a part of the hind-brain
called the cerebellum. It is responsible for precision of voluntary actions
and maintaining the posture and balance of the body. Imagine what
would happen if each of these events failed to take place if we were not
thinking about it.
Figure 6.3
Figure 6.3
Figure 6.3
Figure 6.3
Figure 6.3 Human brain
2024-25 | Science 104 all this, a decision is made about how to respond and the information is passed on to the motor areas which control the movement of voluntary muscles, for example, our leg muscles. However, certain sensations are distinct from seeing or hearing, for example, how do we know that... |
Summarize the following historical passage: | (ix)
CHAIRMAN, ADVISORY GROUP FOR TEXTBOOKS IN SCIENCE AND MATHEMATICS
J.V. Narlikar, Emeritus Professor, Inter-University Centre for Astronomy and
Astrophysics (IUCAA), Ganeshkhind, Pune University, Pune
CHIEF ADVISOR
Rupamanjari Ghosh, Professor, School of Physical Sciences, Jawaharlal Nehru
University, New Delhi
MEMBERS
Alka Mehrotra, Reader, DESM, NCERT, New Delhi
Animesh K. Mohapatra, Reader, Regional Institute of Education, Ajmer
B.B. Swain, Professor (Retd.), Department of Physics, Utkal University, Orissa
B.K. Sharma, Professor, DESM, NCERT, New Delhi
B.K. Tripathi, Reader, DESM, NCERT, New Delhi
Brahm Parkash, Professor, DESM, NCERT, New Delhi
Charu Maini, PGT, Salwan Public School, Gurgaon, Haryana
Dinesh Kumar, Reader, DESM, NCERT, New Delhi
Gagan Gupta, Reader, DESM, NCERT, New Delhi
H.L. Satheesh, TGT , DM School, Regional Institute of Education, Mysore
Ishwant Kaur, PGT, DM School, Regional Institute of Education, Bhopal
J.D. Arora, Reader, Hindu College, Moradabad, Uttar Pradesh
Meenambika Menon, TGT, Cambridge School, Noida, Uttar Pradesh
Puran Chand, Professor and Jt. Director (Retd.), Central Institute of Educational Technology
NCERT, New Delhi
Reeta Sharma, Reader, Regional Institute of Education, Bhopal
R.P. Singh, Lecturer, Rajkiya Pratibha Vikas Vidyalaya, Kishan Ganj, Delhi
Satyajit Rath, Scientist, National Institute of Immunology, JNU Campus, New Delhi
S.K. Dash, Reader, Regional Institute of Education, Bhubaneswar
Sunita Ramrakhiani, PGT, Ahlcon Public School, Delhi
Uma Sudhir, Eklavya, Indore, Madhya Pradesh
Vandana Saxena, TGT, Kendriya Vidyalaya-4, Kandhar Lines, Delhi Cantt., New Delhi
Vinod Kumar, Reader, Hans Raj College, Delhi University, Delhi
MEMBER-COORDINATOR
Anjni Koul, Lecturer, DESM, NCERT, New Delhi
TEXTBOOK DEVELOPMENT COMMITTEE
2024-25 | (ix) CHAIRMAN, ADVISORY GROUP FOR TEXTBOOKS IN SCIENCE AND MATHEMATICS J.V. Narlikar, Emeritus Professor, Inter-University Centre for Astronomy and Astrophysics (IUCAA), Ganeshkhind, Pune University, Pune CHIEF ADVISOR Rupamanjari Ghosh, Professor, School of Physical Sciences, Jawaharlal Nehru University, New Delhi MEMBERS Alka Mehrotra, Reader, DESM, NCERT, New Delhi Animesh K. Mohapatra,... |
Summarize the following historical passage: | Carbon and its Compounds
71
We see that some substances are capable of adding oxygen to others.
These substances are known as oxidising agents.
Alkaline potassium permanganate or acidified potassium dichromate
are oxidising alcohols to acids, that is, adding oxygen to the starting
material. Hence they are known as oxidising agents.
4.3.3 Addition Reaction
Unsaturated hydrocarbons add hydrogen in the presence of catalysts
such as palladium or nickel to give saturated hydrocarbons. Catalysts
are substances that cause a reaction to occur or proceed at a different
rate without the reaction itself being affected. This reaction is commonly
used in the hydrogenation of vegetable oils using a nickel catalyst.
Vegetable oils generally have long unsaturated carbon chains while
animal fats have saturated carbon chains.
You must have seen advertisements stating that some vegetable oils
are ‘healthy’. Animal fats generally contain saturated fatty acids which
are said to be harmful for health. Oils containing unsaturated fatty acids
should be chosen for cooking.
4.3.4 Substitution Reaction
Saturated hydrocarbons are fairly unreactive and are inert in the presence
of most reagents. However, in the presence of sunlight, chlorine is added
to hydrocarbons in a very fast reaction. Chlorine can replace the hydrogen
atoms one by one. It is called a substitution reaction because one type
of atom or a group of atoms takes the place of another. A number of
products are usually formed with the higher homologues of alkanes.
CH4 + Cl2 → CH3Cl + HCl (in the presence of sunlight)
?
Q
U
E
S
T
I
O
N
S
1.
Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
2.
A mixture of oxygen and ethyne is burnt for welding. Can you tell why
a mixture of ethyne and air is not used?
4.4 SOME IMPORTANT CARBON COMPOUNDS – ETHANOL
AND ETHANOIC ACID
Many carbon compounds are invaluable to us. But here we shall study
the properties of two commercially important compounds – ethanol and
ethanoic acid.
2024-25 | Carbon and its Compounds 71 We see that some substances are capable of adding oxygen to others. These substances are known as oxidising agents. Alkaline potassium permanganate or acidified potassium dichromate are oxidising alcohols to acids, that is, adding oxygen to the starting material. Hence they are known as oxidising... |
Summarize the following historical passage: | The Human Eye and the Colourful World
163
(a)
Myopia
Myopia is also known as near-
sightedness. A person with myopia
can see nearby objects clearly but
cannot see distant objects distinctly.
A person with this defect has the far
point nearer than infinity. Such a
person may see clearly upto a
distance of a few metres. In a myopic
eye, the image of a distant object is
formed in front of the retina [Fig.
10.2 (b)] and not at the retina itself.
This defect may arise due to (i)
excessive curvature of the eye lens,
or (ii) elongation of the eyeball. This
defect can be corrected by using a
concave lens of suitable power. This
is illustrated in Fig. 10.2 (c). A
concave lens of suitable power will
bring the image back on to the
retina and thus the defect is corrected.
(b)
Hypermetropia
Hypermetropia is also known as far-sightedness.
A person with hypermetropia can see distant
objects clearly but cannot see nearby objects
distinctly. The near point, for the person, is farther
away from the normal near point (25 cm). Such a
person has to keep a reading material much
beyond 25 cm from the eye for comfortable
reading. This is because the light rays from a
closeby object are focussed at a point behind the
retina as shown in Fig. 10.3 (b). This defect arises
either because (i) the focal length of the eye lens is
too long, or (ii) the eyeball has become too small.
This defect can be corrected by using a convex
lens of appropriate power. This is illustrated in
Fig. 10.3 (c). Eye-glasses with converging lenses
provide the additional focussing power required
for forming the image on the retina.
(c) Presbyopia
The power of accommodation of the eye usually
decreases with ageing. For most people, the near
point gradually recedes away. They find it difficult
to see nearby objects comfortably and distinctly
without corrective eye-glasses. This defect is
called Presbyopia. It arises due to the gradual
Figure 10.2
Figure 10.2
Figure 10.2
Figure 10.2
Figure 10.2
(a), (b) The myopic eye, and (c) correction for myopia with a
concave lens
Figure 10.3
Figure 10.3
Figure 10.3
Figure 10.3
Figure 10.3
(a), (b) The hypermetropic eye, and (c)
correction for hypermetropia
N = Near point of a
hypermetropic eye.
N’ = Near point of a
normal eye.
2024-25 | The Human Eye and the Colourful World 163 (a) Myopia Myopia is also known as near- sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly. A person with this defect has the far point nearer than infinity. Such a person may see clearly... |
Summarize the following historical passage: | Science
2
Activity 1.2
Activity 1.2
Activity 1.2
Activity 1.2
Activity 1.2
Figure 1.2
Figure 1.2
Figure 1.2
Figure 1.2
Figure 1.2
Formation of hydrogen
gas by the action of
dilute sulphuric acid on
zinc
From the above three activities, we can say that any of
the following observations helps us to determine whether
a chemical reaction has taken place –
n
change in state
n
change in colour
n
evolution of a gas
n
change in temperature.
As we observe the changes around us, we can see
that there is a large variety of chemical reactions taking
place around us. We will study about the various types
of chemical reactions and their symbolic representation
in this Chapter.
Activity 1.3
Activity 1.3
Activity 1.3
Activity 1.3
Activity 1.3
n
Take a few zinc granules in a conical flask or a test tube.
n
Add dilute hydrochloric acid or sulphuric acid to this
(Fig. 1.2).
CAUTION: Handle the acid with care.
n
Do you observe anything happening around the zinc
granules?
n
Touch the conical flask or test tube. Is there any change in
its temperature?
n
Take lead nitrate
solution in a test
tube.
n
Add potassium
iodide solution
to this.
n
What do you
observe?
1.1 CHEMIC
1.1 CHEMIC
1.1 CHEMIC
1.1 CHEMIC
1.1 CHEMICAL EQUA
AL EQUA
AL EQUA
AL EQUA
AL EQUATIONS
TIONS
TIONS
TIONS
TIONS
Activity 1.1 can be described as – when a magnesium ribbon is burnt in
oxygen, it gets converted to magnesium oxide. This description of a
chemical reaction in a sentence form is quite long. It can be written in a
shorter form. The simplest way to do this is to write it in the form of a
word-equation.
The word-equation for the above reaction would be –
Magnesium + Oxygen
→Magnesium oxide
(1.1)
(Reactants)
(Product)
The substances that undergo chemical change in the reaction (1.1),
magnesium and oxygen, are the reactants. The new substance is
magnesium oxide, formed during the reaction, as a product.
A word-equation shows change of reactants to products through an
arrow placed between them. The reactants are written on the left-hand
side (LHS) with a plus sign (+) between them. Similarly, products are
written on the right-hand side (RHS) with a plus sign (+) between them.
The arrowhead points towards the products, and shows the direction of
the reaction.
You must have observed that magnesium ribbon burns with a
dazzling white flame and changes into a white powder. This powder is
magnesium oxide. It is formed due to the reaction between magnesium
and oxygen present in the air.
2024-25 | Science 2 Activity 1.2 Activity 1.2 Activity 1.2 Activity 1.2 Activity 1.2 Figure 1.2 Figure 1.2 Figure 1.2 Figure 1.2 Figure 1.2 Formation of hydrogen gas by the action of dilute sulphuric acid on zinc From the above three activities, we can say that any of the following observations helps... |
Summarize the following historical passage: | Electricity
191
11.8 ELECTRIC POWER
11.8 ELECTRIC POWER
11.8 ELECTRIC POWER
11.8 ELECTRIC POWER
11.8 ELECTRIC POWER
You have studied in your earlier Class that the rate of doing work is
power. This is also the rate of consumption of energy.
Equation (11.21) gives the rate at which electric energy is dissipated
or consumed in an electric circuit. This is also termed as electric power.
The power P is given by
P = VI
Or
P = I2R = V2/R
(11.22)
The SI unit of electric power is watt (W). It is the power consumed by
a device that carries 1 A of current when operated at a potential difference
of 1 V. Thus,
1 W = 1 volt × 1 ampere = 1 V A
(11.23)
The unit ‘watt’ is very small. Therefore, in actual practice we use a
much larger unit called ‘kilowatt’. It is equal to 1000 watts. Since electrical
energy is the product of power and time, the unit of electric energy is,
therefore, watt hour (W h). One watt hour is the energy consumed when
1 watt of power is used for 1 hour. The commercial unit of electric energy
is kilowatt hour (kW h), commonly known as ‘unit’.
1 kW h = 1000 watt × 3600 second
= 3.6 × 106 watt second
= 3.6 × 106 joule (J)
More to Know!
Many people think that electrons are consumed in an electric circuit. This is wrong!
We pay the electricity board or electric company to provide energy to move electrons
through the electric gadgets like electric bulb, fan and engines. We pay for the energy
that we use.
Example 11.12
An electric bulb is connected to a 220 V generator. The current is
0.50 A. What is the power of the bulb?
Solution
P
=
VI
=
220 V × 0.50 A
=
110 J/s
=
110 W.
Example 11.13
An electric refrigerator rated 400 W operates 8 hour/day. What is
the cost of the energy to operate it for 30 days at Rs 3.00 per kW h?
2024-25 | Electricity 191 11.8 ELECTRIC POWER 11.8 ELECTRIC POWER 11.8 ELECTRIC POWER 11.8 ELECTRIC POWER 11.8 ELECTRIC POWER You have studied in your earlier Class that the rate of doing work is power. This is also the rate of consumption of energy. Equation (11.21) gives the rate at which electric energy... |
Summarize the following historical passage: | Science
76
Activity 4.11
Activity 4.11
Activity 4.11
Activity 4.11
Activity 4.11
n
Take about 10 mL of distilled water (or rain water) and 10 mL of
hard water (from a tubewell or hand-pump) in separate test tubes.
n
Add a couple of drops of soap solution to both.
n
Shake the test tubes vigorously for an equal period of time and
observe the amount of foam formed.
n
In which test tube do you get more foam?
n
In which test tube do you observe a white curdy precipitate?
Note for the teacher : If hard water is not available in your locality,
prepare some hard water by dissolving hydrogencarbonates/
sulphates/chlorides of calcium or magnesium in water.
Activity 4.12
Activity 4.12
Activity 4.12
Activity 4.12
Activity 4.12
n
Take two test tubes with about 10 mL of hard water in each.
n
Add five drops of soap solution to one and five drops of detergent
solution to the other.
n
Shake both test tubes for the same period.
n
Do both test tubes have the same amount of foam?
n
In which test tube is a curdy solid formed?
?
Q
U
E
S
T
I
O
N
S
1.
Would you be able to check if water is hard by using a detergent?
2.
People use a variety of methods to wash clothes. Usually after adding
the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle,
scrub with a brush or the mixture is agitated in a washing machine.
Why is agitation necessary to get clean clothes?
Have you ever observed while bathing that foam is formed with
difficulty and an insoluble substance (scum) remains after washing with
water? This is caused by the reaction of soap with the calcium and
magnesium salts, which cause the hardness of water. Hence you need
to use a larger amount of soap. This problem is overcome by using
another class of compounds called detergents as cleansing agents.
Detergents are generally sodium salts of sulphonic acids or ammonium
salts with chlorides or bromides ions, etc. Both have long hydrocarbon
chain. The charged ends of these compounds do not form insoluble
precipitates with the calcium and magnesium ions in hard water. Thus,
they remain effective in hard water. Detergents are usually used to make
shampoos and products for cleaning clothes.
2024-25 | Science 76 Activity 4.11 Activity 4.11 Activity 4.11 Activity 4.11 Activity 4.11 n Take about 10 mL of distilled water (or rain water) and 10 mL of hard water (from a tubewell or hand-pump) in separate test tubes. n Add a couple of drops of soap solution to both. n... |
Summarize the following historical passage: | Magnetic Effects of Electric Current
197
Magnetic field is a quantity that has both direction and magnitude.
The direction of the magnetic field is taken to be the direction in which a
north pole of the compass needle moves inside it. Therefore it is taken
by convention that the field lines emerge from north pole and merge at
the south pole (note the arrows marked on the field lines in Fig. 12.4).
Inside the magnet, the direction of field lines is from its south pole to its
north pole. Thus the magnetic field lines are closed curves.
The relative strength of the magnetic field is shown by the degree of
closeness of the field lines. The field is stronger, that is, the force acting
on the pole of another magnet placed is greater where the field lines are
crowded (see Fig. 12.4).
No two field-lines are found to cross each other. If they did, it would
mean that at the point of intersection, the compass needle would point
towards two directions, which is not possible.
12.2
12.2
12.2
12.2
12.2 MA
MA
MA
MA
MAGNETIC FIELD DUE TO A CURRENT
GNETIC FIELD DUE TO A CURRENT
GNETIC FIELD DUE TO A CURRENT
GNETIC FIELD DUE TO A CURRENT
GNETIC FIELD DUE TO A CURRENT-----CCCCCARRYING
ARRYING
ARRYING
ARRYING
ARRYING
CONDUCTOR
CONDUCTOR
CONDUCTOR
CONDUCTOR
CONDUCTOR
In Activity 12.1, we have seen that an electric current through a
metallic conductor produces a magnetic field around it. In order to
find the direction of the field produced let us repeat the activity in the
following way –
Figure 12.3
Figure 12.3
Figure 12.3
Figure 12.3
Figure 12.3
Drawing a magnetic field line with the help of a
compass needle
n
Mark the position of two ends of the needle.
n
Now move the needle to a new position
such that its south pole occupies the
position previously occupied by its north
pole.
n
In this way, proceed step by step till you
reach the south pole of the magnet as
shown in Fig. 12.3.
n
Join the points marked on the paper by a
smooth curve. This curve represents
a field line.
n
Repeat the above procedure and draw as
many lines as you can. You will get a
pattern shown in Fig. 12.4. These lines
represent the magnetic field around the
magnet. These are known as magnetic
field lines.
n
Observe the deflection in the compass
needle as you move it along a field line.
The deflection increases as the needle is
moved towards the poles.
Figure 12.4
Figure 12.4
Figure 12.4
Figure 12.4
Figure 12.4
Field lines around a bar magnet
2024-25 | Magnetic Effects of Electric Current 197 Magnetic field is a quantity that has both direction and magnitude. The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it. Therefore it is taken by convention that the field... |
Summarize the following historical passage: | Science
142
n
Try with plane mirrors of different sizes. Did you see the entire
object in the image?
n
Repeat this Activity with a concave mirror. Did the mirror show
full length image of the object?
n
Now try using a convex mirror. Did you succeed? Explain your
observations with reason.
You can see a full-length image of a tall building/tree in a small
convex mirror. One such mirror is fitted in a wall of Agra Fort facing Taj
Mahal. If you visit the Agra Fort, try to observe the full image of Taj
Mahal. To view distinctly, you should stand suitably at the terrace
adjoining the wall.
Uses of convex mirrors
Convex mirrors are commonly used as rear-view (wing) mirrors in
vehicles. These mirrors are fitted on the sides of the vehicle, enabling the
driver to see traffic behind him/her to facilitate safe driving. Convex
mirrors are preferred because they always give an erect, though
diminished, image. Also, they have a wider field of view as they are curved
outwards. Thus, convex mirrors enable the driver to view much larger
area than would be possible with a plane mirror.
Q
U
E
S
T
I
O
N
S
?
1.
Define the principal focus of a concave mirror.
2.
The radius of curvature of a spherical mirror is 20 cm. What is its focal
length?
3.
Name a mirror that can give an erect and enlarged image of an object.
4.
Why do we prefer a convex mirror as a rear-view mirror in vehicles?
9.2.3 Sign Convention for Reflection by Spherical Mirrors
While dealing with the reflection of light by spherical mirrors, we shall
follow a set of sign conventions called the New Cartesian Sign
Convention. In this convention, the pole (P) of the mirror is taken as the
origin (Fig. 9.9). The principal axis of the mirror is taken as the x-axis
(X’X) of the coordinate system. The conventions are as follows –
(i)
The object is always placed to the left of the mirror. This implies
that the light from the object falls on the mirror from the left-hand
side.
(ii)
All distances parallel to the principal axis are measured from the
pole of the mirror.
(iii)
All the distances measured to the right of the origin (along
+ x-axis) are taken as positive while those measured to the left of
the origin (along – x-axis) are taken as negative.
(iv)
Distances measured perpendicular to and above the principal axis
(along + y-axis) are taken as positive.
(v)
Distances measured perpendicular to and below the principal axis
(along –y-axis) are taken as negative.
2024-25 | Science 142 n Try with plane mirrors of different sizes. Did you see the entire object in the image? n Repeat this Activity with a concave mirror. Did the mirror show full length image of the object? n Now try using a convex mirror. Did you succeed? Explain your observations... |
Summarize the following historical passage: | Electricity
173
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE
What makes the electric charge to flow? Let us consider the analogy of
flow of water. Charges do not flow in a copper wire by themselves, just as
water in a perfectly horizontal tube does not flow. If one end of the tube
is connected to a tank of water kept at a higher level, such that there is a
pressure difference between the two ends of the tube, water flows out of
the other end of the tube. For flow of charges in a conducting metallic
wire, the gravity, of course, has no role to play; the electrons move only
if there is a difference of electric pressure – called the potential difference –
along the conductor. This difference of potential may be produced by a
battery, consisting of one or more electric cells. The chemical action within
a cell generates the potential difference across the terminals of the cell,
even when no current is drawn from it. When the cell is connected to a
conducting circuit element, the potential difference sets the charges in
motion in the conductor and produces an electric current. In order to
maintain the current in a given electric circuit, the cell has to expend its
chemical energy stored in it.
We define the electric potential difference between two points in an
electric circuit carrying some current as the work done to move a unit
charge from one point to the other –
Potential difference (V) between two points = Work done (W)/Charge (Q)
V
=
W/Q
(11.2)
The SI unit of electric potential difference is volt (V), named after
Alessandro Volta (1745 –1827), an Italian physicist. One volt is the
potential difference between two points in a current carrying conductor
when 1 joule of work is done to move a charge of 1 coulomb from one
point to the other.
Therefore, 1 volt =
1 joule
1 coulomb
(11.3)
1 V = 1 J C–1
The potential difference is measured by means of an instrument called
the voltmeter. The voltmeter is always connected in parallel across the
points between which the potential difference is to be measured.
Example 11.2
How much work is done in moving a charge of 2 C across two points
having a potential difference 12 V?
Solution
The amount of charge Q, that flows between two points at potential
difference V (= 12 V) is 2 C. Thus, the amount of work W, done in
moving the charge [from Eq. (11.2)] is
2024-25 | Electricity 173 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE 11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE What makes the electric charge to flow? Let us consider the analogy of flow of water. Charges do... |
Summarize the following historical passage: | Control and Coordination
111
If it is so important that hormones should be secreted in precise
quantities, we need a mechanism through which this is done. The timing
and amount of hormone released are regulated by feedback mechanisms.
For example, if the sugar levels in blood rise, they are detected by the
cells of the pancreas which respond by producing more insulin. As the
blood sugar level falls, insulin secretion is reduced.
Table 6.1 : Some important hormones and their functions
Activity 6.4
Activity 6.4
Activity 6.4
Activity 6.4
Activity 6.4
n Hormones are secreted by endocrine glands and have specific functions. Complete
Table 6.1 based on the hormone, the endocrine gland or the functions provided.
Q
U
E
S
T
I
O
N
S
1.
How does chemical coordination take place in animals?
2.
Why is the use of iodised salt advisable?
3.
How does our body respond when adrenaline is secreted into the blood?
4.
Why are some patients of diabetes treated by giving injections of insulin?
What you have learnt
?
n
Control and coordination are the functions of the nervous system and hormones
in our bodies.
n
The responses of the nervous system can be classified as reflex action, voluntary
action or involuntary action.
n
The nervous system uses electrical impulses to transmit messages.
n
The nervous system gets information from our sense organs and acts through our
muscles.
n
Chemical coordination is seen in both plants and animals.
n
Hormones produced in one part of an organism move to another part to achieve
the desired effect.
n
A feedback mechanism regulates the action of the hormones.
S.No.
Hormone
Endocrine Gland
Functions
1.
Growth hormone
Pituitary gland
Stimulates growth in all organs
2.
Thyroid gland
Regulates metabolism for body growth
3.
Insulin
Regulates blood sugar level
4.
Testosterone
Testes
5.
Ovaries
Development of female sex organs,
regulates menstrual cycle, etc.
6.
Adrenaline
Adrenal gland
7.
Releasing
Stimulates pituitary gland to release
hormones
hormones
2024-25 | Control and Coordination 111 If it is so important that hormones should be secreted in precise quantities, we need a mechanism through which this is done. The timing and amount of hormone released are regulated by feedback mechanisms. For example, if the sugar levels in blood rise, they are detected... |
Summarize the following historical passage: | How do Organisms Reproduce?
123
participate in this process of mating, their state of sexual maturity must
be identifiable by other individuals. Many changes during puberty, such
as new hair-growth patterns, are signals that sexual maturation is taking
place.
On the other hand, the actual transfer of germ-cells between two
people needs special organs for the sexual act, such as the penis when it
is capable of becoming erect. In mammals such as humans, the baby is
carried in the mother’s body for a long period, and will be breast-fed
later. The female reproductive organs and breasts will need to mature to
accommodate these possibilities. Let us look at the systems involved in
the process of sexual reproduction.
7.3.3 (a) Male Reproductive System
The male reproductive system (Fig. 7.10)
consists of portions which produce the
germ-cells and other portions that deliver
the germ-cells to the site of fertilisation.
The formation of germ-cells or sperms
takes place in the testes. These are located
outside the abdominal cavity in scrotum
because sperm formation requires a lower
temperature than the normal body
temperature. We have discussed the role of the
testes in the secretion of the hormone,
testosterone, in the previous chapter. In
addition to regulating the formation of sperms,
testosterone brings about changes in
appearance seen in boys at the time of puberty.
The sperms formed are delivered
through the vas deferens which unites with
a tube coming from the urinary bladder. The
urethra thus forms a common passage for
both the sperms and urine. Along the path
of the vas deferens, glands like the prostate
and the seminal vesicles add their secretions
so that the sperms are now in a fluid which
makes their transport easier and this fluid
also provides nutrition. The sperms are tiny
bodies that consist of mainly genetic
material and a long tail that helps them to
move towards the female germ-cell.
7.3.3 (b) Female Reproductive System
The female germ-cells or eggs are made in
the ovaries. They are also responsible for the
production of some hormones. Look at
Fig. 7.11 and identify the various organs in
the female reproductive system.
Figure 7.10
Figure 7.10
Figure 7.10
Figure 7.10
Figure 7.10 Human–male reproductive system
Figure 7.11
Figure 7.11
Figure 7.11
Figure 7.11
Figure 7.11 Human –female reproductive system
2024-25 | How do Organisms Reproduce? 123 participate in this process of mating, their state of sexual maturity must be identifiable by other individuals. Many changes during puberty, such as new hair-growth patterns, are signals that sexual maturation is taking place. On the other hand, the actual transfer of germ-cells between two... |
Summarize the following historical passage: | Science
44
Metal + Dilute acid → Salt + Hydrogen
But do all metals react in the same manner? Let us find out.
Activity 3.11
Activity 3.11
Activity 3.11
Activity 3.11
Activity 3.11
n
Collect all the metal samples except sodium and potassium again.
If the samples are tarnished, rub them clean with sand paper.
CAUTION: Do not take sodium and potassium as they react
vigorously even with cold water.
n
Put the samples separately in test tubes containing dilute
hydrochloric acid.
n
Suspend thermometers in the test tubes, so that their bulbs are
dipped in the acid.
n
Observe the rate of formation of bubbles carefully.
n
Which metals reacted vigorously with dilute hydrochloric acid?
n
With which metal did you record the highest temperature?
n
Arrange the metals in the decreasing order of reactivity with dilute
acids.
Write equations for the reactions of magnesium, aluminium, zinc
and iron with dilute hydrochloric acid.
Hydrogen gas is not evolved when a metal reacts with nitric acid. It is
because HNO3 is a strong oxidising agent. It oxidises the H2 produced to
water and itself gets reduced to any of the nitrogen oxides (N2O, NO,
NO2). But magnesium (Mg) and manganese (Mn) react with very dilute
HNO3 to evolve H2 gas.
You must have observed in Activity 3.11, that the rate of formation
of bubbles was the fastest in the case of magnesium. The reaction was
also the most exothermic in this case. The reactivity decreases in the
order Mg > Al > Zn > Fe. In the case of copper, no bubbles were seen and
the temperature also remained unchanged. This shows that copper does
not react with dilute HCl.
Do You Know?
Aqua regia, (Latin for ‘royal water’) is a freshly prepared mixture of concentrated
hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve
gold, even though neither of these acids can do so alone. Aqua regia is a highly
corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and
platinum.
3.2.4 How do Metals react with Solutions of other Metal
Salts?
Activity 3.12
Activity 3.12
Activity 3.12
Activity 3.12
Activity 3.12
n
Take a clean wire of copper and an iron nail.
n
Put the copper wire in a solution of iron sulphate and the iron
nail in a solution of copper sulphate taken in test tubes (Fig. 3.4).
n
Record your observations after 20 minutes.
2024-25 | Science 44 Metal + Dilute acid → Salt + Hydrogen But do all metals react in the same manner? Let us find out. Activity 3.11 Activity 3.11 Activity 3.11 Activity 3.11 Activity 3.11 n Collect all the metal samples except sodium and potassium again. If the samples are tarnished, rub... |
Summarize the following historical passage: | Science
88888
Figure 1.5
Heating of lead nitrate and
emission of nitrogen dioxide
Figure 1.4
Correct way of heating
the boiling tube
containing crystals
of ferrous sulphate
and of smelling the
odour
Activity 1.6
Activity 1.6
Activity 1.6
Activity 1.6
Activity 1.6
n
Take about 2 g lead nitrate powder in a boiling
tube.
n
Hold the boiling tube with a pair of tongs and
heat it over a flame, as shown in Fig. 1.5.
n
What do you observe? Note down the change,
if any.
You will observe the emission of brown fumes.
These fumes are of nitrogen dioxide (NO2). The
reaction that takes place is –
Activity 1.5
Activity 1.5
Activity 1.5
Activity 1.5
Activity 1.5
n
Take about 2 g ferrous sulphate crystals
in a dry boiling tube.
n
Note the colour of the ferrous sulphate
crystals.
n
Heat the boiling tube over the flame of
a burner or spirit lamp as shown in
Fig. 1.4.
n
Observe the colour of the crystals after
heating.
Have you noticed that the green colour of the ferrous sulphate crystals
has changed? You can also smell the characteristic odour of burning
sulphur.
2FeSO4(s)
Heat
→
Fe2O3(s) + SO2(g) + SO3(g)
(1.19)
(Ferrous sulphate)
(Ferric oxide)
In this reaction you can observe that a single reactant breaks down
to give simpler products. This is a decomposition reaction. Ferrous
sulphate crystals (FeSO4. 7H2O) lose water when heated and the colour
of the crystals changes. It then decomposes to ferric oxide (Fe2O3),
sulphur dioxide (SO2) and sulphur trioxide (SO3). Ferric oxide is a solid,
while SO2 and SO3 are gases.
Decomposition of calcium carbonate to calcium oxide and carbon
dioxide on heating is an important decomposition reaction used in
various industries. Calcium oxide is called lime or quick lime. It has
many uses – one is in the manufacture of cement. When a decomposition
reaction is carried out by heating, it is called thermal decomposition.
CaCO3(s)
Heat
→
CaO(s) + CO2(g)
(1.20)
(Limestone)
(Quick lime)
Another example of a thermal decomposition reaction is given
in Activity 1.6.
1.2.2 Decomposition Reaction
2024-25 | Science 88888 Figure 1.5 Heating of lead nitrate and emission of nitrogen dioxide Figure 1.4 Correct way of heating the boiling tube containing crystals of ferrous sulphate and of smelling the odour Activity 1.6 Activity 1.6 Activity 1.6 Activity 1.6 Activity 1.6 n Take about 2 g lead nitrate powder... |
Summarize the following historical passage: | Heredity
133
Q
U
E
S
T
I
O
N
S
?
1.
How do Mendel’s experiments show that traits may be dominant or
recessive?
2.
How do Mendel’s experiments show that traits are inherited
independently?
3.
A man with blood group A marries a woman with blood group O and
their daughter has blood group O. Is this information enough to tell you
which of the traits – blood group A or O – is dominant? Why or why not?
4.
How is the sex of the child determined in human beings?
What you have learnt
n
Variations arising during the process of reproduction can be inherited.
n
These variations may lead to increased survival of the individuals.
n
Sexually reproducing individuals have two copies of genes for the same trait. If the
copies are not identical, the trait that gets expressed is called the dominant trait
and the other is called the recessive trait.
n
Traits in one individual may be inherited separately, giving rise to new combinations
of traits in the offspring of sexual reproduction.
n
Sex is determined by different factors in various species. In human beings, the
sex of the child depends on whether the paternal chromosome is X (for girls) or Y
(for boys).
E
X
E
R
C
I
S
E
S
1.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers
with short pea plants bearing white flowers. The progeny all bore violet flowers,
but almost half of them were short. This suggests that the genetic make-up of the
tall parent can be depicted as
(a)
TTWW
(b)
TTww
(c)
TtWW
(d)
TtWw
2.
A study found that children with light-coloured eyes are likely to have parents
with light-coloured eyes. On this basis, can we say anything about whether the
light eye colour trait is dominant or recessive? Why or why not?
3.
Outline a project which aims to find the dominant coat colour in dogs.
4.
How is the equal genetic contribution of male and female parents ensured in
the progeny?
2024-25 | Heredity 133 Q U E S T I O N S ? 1. How do Mendel’s experiments show that traits may be dominant or recessive? 2. How do Mendel’s experiments show that traits are inherited independently? 3. A man with blood group A marries a woman with blood group O... |
Summarize the following historical passage: | Light – Reflection and Refraction
159
n
Mirror formula,
1
1
1
+
=
v
u
f , gives the relationship between the object-distance (u),
image-distance (v), and focal length (f) of a spherical mirror.
n
The focal length of a spherical mirror is equal to half its radius of curvature.
n
The magnification produced by a spherical mirror is the ratio of the height of the
image to the height of the object.
n
A light ray travelling obliquely from a denser medium to a rarer medium bends
away from the normal. A light ray bends towards the normal when it travels obliquely
from a rarer to a denser medium.
n
Light travels in vacuum with an enormous speed of 3×108 m s-1. The speed of light
is different in different media.
n
The refractive index of a transparent medium is the ratio of the speed of light in
vacuum to that in the medium.
n
In case of a rectangular glass slab, the refraction takes place at both air-glass
interface and glass-air interface. The emergent ray is parallel to the direction of
incident ray.
n
Lens formula,
1
1
1
–
=
v
u
f , gives the relationship between the object-distance (u),
image-distance (v), and the focal length (f) of a spherical lens.
n
Power of a lens is the reciprocal of its focal length. The SI unit of power of a lens is
dioptre.
E
X
E
R
C
I
S
E
S
1.
Which one of the following materials cannot be used to make a lens?
(a)
Water
(b)
Glass
(c)
Plastic
(d)
Clay
2.
The image formed by a concave mirror is observed to be virtual, erect and larger
than the object. Where should be the position of the object?
(a)
Between the principal focus and the centre of curvature
(b)
At the centre of curvature
(c)
Beyond the centre of curvature
(d)
Between the pole of the mirror and its principal focus.
3.
Where should an object be placed in front of a convex lens to get a real image of the
size of the object?
(a)
At the principal focus of the lens
(b)
At twice the focal length
(c)
At infinity
(d)
Between the optical centre of the lens and its principal focus.
4.
A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The
mirror and the lens are likely to be
(a)
both concave.
(b)
both convex.
2024-25 | Light – Reflection and Refraction 159 n Mirror formula, 1 1 1 + = v u f , gives the relationship between the object-distance (u), image-distance (v), and focal length (f) of a spherical mirror. n The focal length of a spherical mirror is equal to half its radius of... |
Summarize the following historical passage: | (x)
A C K N O W L E D G E M E N T S
The National Council of Educational Research and Training (NCERT), besides expressing
its gratefulness towards the members of the Textbook Development Committee for their
contribution in the development of the Science Textbook for Class X, also acknowledges
the contribution of the following members for reviewing, editing, refining, and finalisation
of the manuscript of the book. Kanhiya Lal, Principal (Retd.), Directorate of Education,
NCT, Delhi; Ranveer Singh, Lecturer, Sarvodaya Bal Vidyalaya, Timarpur, Delhi; Bharat
Poorey, Professor (Retd.), Govt. Post Graduate College, Indore; Gagandeep Bajaj, Lecturer,
S.P.M. College, Delhi University, Delhi; Ravinder Kaur, TGT, Kendriya Vidyalaya, Rohini,
Delhi; Renu Puri, TGT, N.C. Jindal Public School, New Delhi; Sarita Kumar, Reader,
Acharya Narendra Dev College, Delhi University, Delhi; Shashi Prabha, Lecturer, DESM,
NCERT, Delhi; Rashmi Sharma, Lecturer, NERIE, Shillong; Sushma Jaireth, Reader, DWS,
NCERT, New Delhi; Y.P. Purang, Addl. Director of Education (Retd.), NCT, Delhi; Neeta
Agarwal, TGT, D.L.D.A.V. Model School, Pitampura, Delhi; Roma Anand, TGT, D.L.D.A.V.,
Pitampura, Delhi; Veer Pal Singh, Reader, DEME, NCERT, New Delhi and S.L. Varte,
Lecturer, DESM, NCERT, New Delhi.
The Council also acknowledges the valuable contribution of Sunita Farkya (Professor,
DESM), Pushplata Verma (Assistant Professor, DESM), K.C. Tripathi (Professor, DEL)
and Jatindra Mohan Misra (Professor, DEL) in updating Chapter 16 titled "Sustainable
Management of Natural Resources", and also in the review of this textbook.
The contribution of R.S. Sindhu, Professor (Retd.), DESM; V.P. Srivastava, Professor
(Retd.), DESM; R.K. Parashar, Rachna Garg (Professors, DESM); V.V. Anand, Professor
(Retd.), RIE Mysore; S.V. Sharma (Professor, RIE Mysore); V.P. Singh (Professor, RIE Ajmer);
R. Joshi, Associate Professor (Retd.), DESM; C.V. Shimray, Ruchi Verma (Associate
Professors, DESM); Ram Babu Pareek (Associate Professor, RIE Ajmer); A.K. Srivastava,
Rejaul Karim Barbhuiya, Pramila Tanwar (Assistant Professors, DESM); R.R. Koireng
(Assistant Professor, DCS); V. Tangpu (Assistant Professor, RIE Mysore) and Akhileshwar
Mishra (Head Master, DMS, RIE Bhubaneswar), in the review of this textbook in 2017-18
are acknowledged.
Special thanks are due to Hukum Singh, Professor and Former Head, DESM, NCERT,
New Delhi, for providing all academic and administrative support.
The Council also gratefully acknowledges the support provided by the APC Office of
DESM, administrative staff of DESM; Deepak Kapoor, Incharge, Computer Station, DESM;
Saima and Arvind Sharma, DTP Operators and Rajesh Handa, Illustrator;
Mohd. Qamar Tabrez and Musarrat Parveen, Copy Editors; Seema Yadav, Proof Reader.
The efforts of the Publication Department, NCERT are also highly appreciated.
2024-25 | (x) A C K N O W L E D G E M E N T S The National Council of Educational Research and Training (NCERT), besides expressing its gratefulness towards the members of the Textbook Development Committee for their contribution in the development of the Science Textbook for Class... |
Summarize the following historical passage: | (iv)
the National Monitoring Committee, appointed by the Department of Secondary and
Higher Education, Ministry of Human Resource Development under the Chairmanship
of Professor Mrinal Miri and Professor G.P. Deshpande, for their valuable time and
contribution. As an organisation committed to systemic reform and continuous
improvement in the quality of its products, NCERT welcomes comments and suggestions
which will enable us to undertake further revision and refinement.
Director
New Delhi
National Council of Educational
20 November 2006
Research and Training
2024-25 | (iv) the National Monitoring Committee, appointed by the Department of Secondary and Higher Education, Ministry of Human Resource Development under the Chairmanship of Professor Mrinal Miri and Professor G.P. Deshpande, for their valuable time and contribution. As an organisation committed to systemic reform and continuous improvement in the quality of... |
Summarize the following historical passage: | Carbon and its Compounds
59
saw how the nature of bonding in ionic compounds explains these
properties. Let us now study the properties of some carbon compounds.
Most carbon compounds are poor conductors of electricity as we
have seen in Chapter 2. From the data
given in Table 4.1 on the boiling and
melting points of the carbon compounds,
we find that these compounds have low
melting and boiling points as compared
to ionic compounds (Chapter 3). We can
conclude that the forces of attraction
between the molecules are not very
strong. Since these compounds are
largely non-conductors of electricity, we
can conclude that the bonding in these
compounds does not give rise to any ions.
In Class IX, we learnt about the
combining capacity of various elements and how it depends on the
number of valence electrons. Let us now look at the electronic
configuration of carbon. The atomic number of carbon is 6. What would
be the distribution of electrons in various shells of carbon? How many
valence electrons will carbon have?
We know that the reactivity of elements is explained as their tendency
to attain a completely filled outer shell, that is, attain noble gas
configuration. Elements forming ionic compounds achieve this by either
gaining or losing electrons from the outermost shell. In the case of carbon,
it has four electrons in its outermost shell and needs to gain or lose four
electrons to attain noble gas configuration. If it were to gain or lose
electrons –
(i)
It could gain four electrons forming C4– anion. But it would be difficult
for the nucleus with six protons to hold on to ten electrons, that is,
four extra electrons.
(ii)
It could lose four electrons forming C4+ cation. But it would require
a large amount of energy to remove four electrons leaving behind a
carbon cation with six protons in its nucleus holding on to just two
electrons.
Carbon overcomes this problem by sharing its valence electrons with
other atoms of carbon or with atoms of other elements. Not just carbon,
but many other elements form molecules by sharing electrons in this
manner. The shared electrons ‘belong’ to the outermost shells of both
the atoms and lead to both atoms attaining the noble gas configuration.
Before going on to compounds of carbon, let us look at some simple
molecules formed by the sharing of valence electrons.
The simplest molecule formed in this manner is that of hydrogen.
As you have learnt earlier, the atomic number of hydrogen is 1. Hence
hydrogen has one electron in its K shell and it requires one more electron
to fill the K shell. So two hydrogen atoms share their electrons to form a
molecule of hydrogen, H2. This allows each hydrogen atom to attain the
Table 4.1 Melting points and boiling points of some
compounds of carbon
Compound
Melting
Boiling
point (K)
point (K)
Acetic acid (CH3COOH)
290
391
Chloroform (CHCl3)
209
334
Ethanol (CH3CH2OH)
156
351
Methane (CH4)
90
111
2024-25 | Carbon and its Compounds 59 saw how the nature of bonding in ionic compounds explains these properties. Let us now study the properties of some carbon compounds. Most carbon compounds are poor conductors of electricity as we have seen in Chapter 2. From the data given in Table 4.1 on... |
Summarize the following historical passage: | Metals and Non-metals
53
metal from the electrolyte is deposited on the cathode. The soluble
impurities go into the solution, whereas, the insoluble impurities settle
down at the bottom of the anode and are known as anode mud.
1.
Define the following terms.
(i)
Mineral
(ii) Ore
(iii) Gangue
2.
Name two metals which are found in nature in the free state.
3.
What chemical process is used for obtaining a metal from its oxide?
Activity 3.14
Activity 3.14
Activity 3.14
Activity 3.14
Activity 3.14
n
Take three test tubes and place clean iron nails
in each of them.
n
Label these test tubes A, B and C. Pour some
water in test tube A and cork it.
n
Pour boiled distilled water in test tube B, add
about 1 mL of oil and cork it. The oil will float on
water and prevent the air from dissolving in the
water.
n
Put some anhydrous calcium chloride in
test tube C and cork it. Anhydrous calcium
chloride will absorb the moisture, if any, from
the air. Leave these test tubes for a few days and
then observe (Fig. 3.13).
Figure 3.13
Figure 3.13
Figure 3.13
Figure 3.13
Figure 3.13
Investigating the conditions under which iron
rusts. In tube A, both air and water are
present. In tube B, there is no air dissolved
in the water. In tube C, the air is dry.
You will observe that iron nails rust in test tube A,
but they do not rust in test tubes B and C. In the test
tube A, the nails are exposed to both air and water. In
the test tube B, the nails are exposed to only water, and
the nails in test tube C are exposed to dry air. What
does this tell us about the conditions under which iron
articles rust?
Q
U
E
S
T
I
O
N
S
?
3.5 CORROSION
3.5 CORROSION
3.5 CORROSION
3.5 CORROSION
3.5 CORROSION
You have learnt the following about corrosion in Chapter 1 –
n Silver articles become black after some time when exposed to air.
This is because it reacts with sulphur in the air to form a coating
of silver sulphide.
n Copper reacts with moist carbon dioxide in the air and slowly loses
its shiny brown surface and gains a green coat. This green
substance is basic copper carbonate.
n Iron when exposed to moist air for a long time acquires a coating
of a brown flaky substance called rust.
Let us find out the conditions under which iron rusts.
A
B
C
2024-25 | Metals and Non-metals 53 metal from the electrolyte is deposited on the cathode. The soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are known as anode mud. 1. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue 2.... |
Summarize the following historical passage: | How do Organisms Reproduce?
119
All the modes of reproduction that we have discussed so far allow
new generations to be created from a single individual. This is known as
asexual reproduction.
Q
U
E
S
T
I
O
N
S
?
1.
How does binary fission differ from multiple fission?
2.
How will an organism be benefited if it reproduces through spores?
3.
Can you think of reasons why more complex organisms cannot give
rise to new individuals through regeneration?
4.
Why is vegetative propagation practised for growing some types of
plants?
5.
Why is DNA copying an essential part of the process of reproduction?
7.3 SEXUAL REPRODUCTION
7.3 SEXUAL REPRODUCTION
7.3 SEXUAL REPRODUCTION
7.3 SEXUAL REPRODUCTION
7.3 SEXUAL REPRODUCTION
We are also familiar with modes of reproduction that depend on the
involvement of two individuals before a new generation can be created.
Bulls alone cannot produce new calves, nor can hens alone produce
new chicks. In such cases, both sexes, males and females, are needed to
produce new generations. What is the significance of this sexual mode
of reproduction? Are there any limitations of the asexual mode of
reproduction, which we have been discussing above?
7.3.1 Why the Sexual Mode of Reproduction?
The creation of two new cells from one involves copying of the DNA as
well as of the cellular apparatus. The DNA copying mechanism, as we
have noted, cannot be absolutely accurate, and the resultant errors are
a source of variations in populations of organisms. Every individual
organism cannot be protected by variations, but in a population,
variations are useful for ensuring the survival of the species. It would
therefore make sense if organisms came up with reproductive modes
that allowed more and more variation to be generated.
While DNA-copying mechanisms are not absolutely accurate, they
are precise enough to make the generation of variation a fairly slow
process. If the DNA copying mechanisms were to be less accurate, many
of the resultant DNA copies would not be able to work with the cellular
apparatus, and would die. So how can the process of making variants
be speeded up? Each new variation is made in a DNA copy that already
has variations accumulated from previous generations. Thus, two
different individuals in a population would have quite different patterns
of accumulated variations. Since all of these variations are in living
individuals, it is assured that they do not have any really bad effects.
Combining variations from two or more individuals would thus create
new combinations of variants. Each combination would be novel, since
it would involve two different individuals. The sexual mode of
2024-25 | How do Organisms Reproduce? 119 All the modes of reproduction that we have discussed so far allow new generations to be created from a single individual. This is known as asexual reproduction. Q U E S T I O N S ? 1. How does binary fission differ from multiple... |
Summarize the following historical passage: | Electricity
177
In this Activity we observe that the current is different for different
components. Why do they differ? Certain components offer an easy path
for the flow of electric current while the others resist the flow. We know
that motion of electrons in an electric circuit constitutes an electric
current. The electrons, however, are not completely free to move within a
conductor. They are restrained by the attraction of the atoms among
which they move. Thus, motion of electrons through a conductor is
retarded by its resistance. A component of a given size that offers a low
resistance is a good conductor. A conductor having some appreciable
resistance is called a resistor. A component of identical size that offers a
higher resistance is a poor conductor. An insulator of the same size offers
even higher resistance.
11.5 FA
11.5 FA
11.5 FA
11.5 FA
11.5 FACTORS ON WHICH THE RESIST
CTORS ON WHICH THE RESIST
CTORS ON WHICH THE RESIST
CTORS ON WHICH THE RESIST
CTORS ON WHICH THE RESISTANCE OF A
ANCE OF A
ANCE OF A
ANCE OF A
ANCE OF A
CONDUCTOR DEPENDS
CONDUCTOR DEPENDS
CONDUCTOR DEPENDS
CONDUCTOR DEPENDS
CONDUCTOR DEPENDS
Figure 11.4
Figure 11.4
Figure 11.4
Figure 11.4
Figure 11.4
n
Complete the circuit by connecting the nichrome wire in the gap XY. Plug the key. Note
down the ammeter reading. Take out the key from the plug. [Note: Always take out the key
from the plug after measuring the current through the circuit.]
n
Replace the nichrome wire with the torch bulb in the circuit and find the current through
it by measuring the reading of the ammeter.
n
Now repeat the above step with the 10 W bulb in the gap XY.
n
Are the ammeter readings different for different components connected in the gap XY?
What do the above observations indicate?
n
You may repeat this Activity by keeping any material component in the gap. Observe the
ammeter readings in each case. Analyse the observations.
Activity 11.3
Activity 11.3
Activity 11.3
Activity 11.3
Activity 11.3
n
Complete an electric circuit consisting of a cell, an ammeter, a nichrome wire of length l
[say, marked (1)] and a plug key, as shown in Fig. 11.5.
2024-25 | Electricity 177 In this Activity we observe that the current is different for different components. Why do they differ? Certain components offer an easy path for the flow of electric current while the others resist the flow. We know that motion of electrons in an electric circuit constitutes an electric... |
Summarize the following historical passage: | Science
126
What you have learnt
n
Reproduction, unlike other life processes, is not essential to maintain the life of an
individual organism.
n
Reproduction involves creation of a DNA copy and additional cellular apparatus
by the cell involved in the process.
n
Various organisms use different modes of reproduction depending on their body
design.
n
In fission, many bacteria and protozoa simply divide into two or more daughter
cells.
n
Organisms such as hydra can regenerate if they are broken into pieces. They can
also give out buds which mature into new individuals.
n
Roots, stems and leaves of some plants develop into new plants through vegetative
propagation.
n
These are examples of asexual reproduction where new generations are created
from a single individual.
n
Sexual reproduction involves two individuals for the creation of a new individual.
n
DNA copying mechanisms creates variations which are useful for ensuring the
survival of the species. Modes of sexual reproduction allow for greater variation to
be generated.
n
Reproduction in flowering plants involves transfer of pollen grains from the anther
to the stigma which is referred to as pollination. This is followed by fertilisation.
n
Changes in the body at puberty, such as increase in breast size in girls and new
facial hair growth in boys, are signs of sexual maturation.
n
The male reproductive system in human beings consists of testes which produce
sperms, vas deferens, seminal vesicles, prostate gland, urethra and penis.
n
The female reproductive system in human beings consists of ovaries, fallopian
tubes, uterus and vagina.
n
Sexual reproduction in human beings involves the introduction of sperm in the
vagina of the female. Fertilisation occurs in the fallopian tube.
n
Contraception to avoid pregnancy can be achieved by the use of condoms, oral
pills, copper-T and other methods.
Q
U
E
S
T
I
O
N
S
?
1.
How is the process of pollination different from fertilisation?
2.
What is the role of the seminal vesicles and the prostate gland?
3.
What are the changes seen in girls at the time of puberty?
4.
How does the embryo get nourishment inside the mother’s body?
5.
If a woman is using a copper-T, will it help in protecting her from
sexually transmitted diseases?
2024-25 | Science 126 What you have learnt n Reproduction, unlike other life processes, is not essential to maintain the life of an individual organism. n Reproduction involves creation of a DNA copy and additional cellular apparatus by the cell involved in the process. n Various organisms use different modes of reproduction... |
Summarize the following historical passage: | Science
188
11.7 HEA
11.7 HEA
11.7 HEA
11.7 HEA
11.7 HEATING EFFECT OF ELECTRIC CURRENT
TING EFFECT OF ELECTRIC CURRENT
TING EFFECT OF ELECTRIC CURRENT
TING EFFECT OF ELECTRIC CURRENT
TING EFFECT OF ELECTRIC CURRENT
We know that a battery or a cell is a source of electrical energy. The
chemical reaction within the cell generates the potential difference between
its two terminals that sets the electrons in motion to flow the current
through a resistor or a system of resistors connected to the battery. We
have also seen, in Section 11.2, that to maintain the current, the source
has to keep expending its energy. Where does this energy go? A part of
the source energy in maintaining the current may be consumed into
useful work (like in rotating the blades of an electric fan). Rest of the
source energy may be expended in heat to raise the temperature of
gadget. We often observe this in our everyday life. For example, an electric
fan becomes warm if used continuously for longer time etc. On the other
hand, if the electric circuit is purely resistive, that is, a configuration of
resistors only connected to a battery; the source energy continually gets
dissipated entirely in the form of heat. This is known as the heating
effect of electric current. This effect is utilised in devices such as electric
heater, electric iron etc.
Consider a current I flowing through a resistor of resistance R. Let
the potential difference across it be V (Fig. 11.13). Let t be the time during
which a charge Q flows across. The work done in moving the charge Q
through a potential difference V is VQ. Therefore, the source must supply
energy equal to VQ in time t. Hence the power input to the circuit by the
source is
P
V
VI
=
Q
t =
(11.19)
Or the energy supplied to the circuit by the source in time t is P × t,
that is, VIt. What happens to this energy expended by the source? This
energy gets dissipated in the resistor as heat. Thus for a steady
current I, the amount of heat H produced in time t is
H = VIt
(11.20)
Q
U
E
S
T
I
O
N
S
?
1.
Judge the equivalent resistance when the following are connected in
parallel – (a) 1 Ω and 106 Ω, (b) 1 Ω and 103 Ω, and 106 Ω.
2.
An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water
filter of resistance 500 Ω are connected in parallel to a 220 V source.
What is the resistance of an electric iron connected to the same source
that takes as much current as all three appliances, and what is the
current through it?
3.
What are the advantages of connecting electrical devices in parallel
with the battery instead of connecting them in series?
4.
How can three resistors of resistances 2 Ω, 3 Ω, and 6 Ω be connected
to give a total resistance of (a) 4 Ω, (b) 1 Ω?
5.
What is (a) the highest, (b) the lowest total resistance that can be secured
by combinations of four coils of resistance 4 Ω, 8 Ω, 12 Ω, 24 Ω?
2024-25 | Science 188 11.7 HEA 11.7 HEA 11.7 HEA 11.7 HEA 11.7 HEATING EFFECT OF ELECTRIC CURRENT TING EFFECT OF ELECTRIC CURRENT TING EFFECT OF ELECTRIC CURRENT TING EFFECT OF ELECTRIC CURRENT TING EFFECT OF ELECTRIC CURRENT We know that a battery or a cell is a source of electrical energy.... |
Summarize the following historical passage: | Science
32
What does 10H2O signify? Does it make Na2CO3 wet? We will address
this question in the next section.
Sodium carbonate and sodium hydrogencarbonate are useful
chemicals for many industrial processes as well.
Uses of washing soda
(i)
Sodium carbonate (washing soda) is used in glass, soap and
paper industries.
(ii)
It is used in the manufacture of sodium compounds such as borax.
(iii)
Sodium carbonate can be used as a cleaning agent for domestic
purposes.
(iv)
It is used for removing permanent hardness of water.
2.4.4 Are the Crystals of Salts really Dry?
Activity 2.15
Activity 2.15
Activity 2.15
Activity 2.15
Activity 2.15
n
Heat a few crystals of copper sulphate
in a dry boiling tube.
n
What is the colour of the copper
sulphate after heating?
n
Do you notice water droplets in the
boiling tube? Where have these come
from?
n
Add 2-3 drops of water on the sample
of copper sulphate obtained after
heating.
n
What do you observe? Is the blue
colour of copper sulphate restored?
Figure 2.9
Figure 2.9
Figure 2.9
Figure 2.9
Figure 2.9
Removing water
of crystallisation
Copper sulphate crystals which seem to be dry contain water of
crystallisation. When we heat the crystals, this water is removed and the
salt turns white.
If you moisten the crystals again with water, you will find that blue
colour of the crystals reappears.
Water of crystallisation is the fixed number of water molecules present
in one formula unit of a salt. Five water molecules are present in one
formula unit of copper sulphate. Chemical formula for hydrated copper
sulphate is Cu SO4. 5H2O. Now you would be able to answer the question
whether the molecule of Na2CO3.10H2O is wet.
One other salt, which possesses water of crystallisation is gypsum.
It has two water molecules as water of cyrstallisation. It has the chemical
formula CaSO4.2H2O. Let us look into the use of this salt.
Plaster of Paris
On heating gypsum at 373 K, it loses water molecules and becomes
calcium sulphate hemihydrate (
4
2
1
CaSO .
H O
2
). This is called Plaster of
2024-25 | Science 32 What does 10H2O signify? Does it make Na2CO3 wet? We will address this question in the next section. Sodium carbonate and sodium hydrogencarbonate are useful chemicals for many industrial processes as well. Uses of washing soda (i) Sodium carbonate (washing soda) is used in glass, soap and paper... |
Summarize the following historical passage: | Science
36
(II) Preparing a soda-acid fire extinguisher
The reaction of acids with metal hydrogencarbonates is used in the fire extinguishers
which produce carbon dioxide.
n
Take 20 mL of sodium hydrogencarbonate (NaHCO3) solution in a wash-bottle.
n
Suspend an ignition tube containing dilute sulphuric acid in the wash-bottle
(Fig. 2.10).
n
Close the mouth of the wash-bottle.
n
Tilt the wash-bottle so that the acid from the ignition tube mixes with the sodium
hydrogencarbonate solution below.
n
You will notice discharge coming out of the nozzle.
n
Direct this discharge on a burning candle. What happens?
Figure 2.10
Figure 2.10
Figure 2.10
Figure 2.10
Figure 2.10 (a) Ignition tube containing dilute sulphuric acid suspended in a wash-bottle containing
sodium hydrogencarbonate, (b) Discharge coming out of the nozzle
2024-25 | Science 36 (II) Preparing a soda-acid fire extinguisher The reaction of acids with metal hydrogencarbonates is used in the fire extinguishers which produce carbon dioxide. n Take 20 mL of sodium hydrogencarbonate (NaHCO3) solution in a wash-bottle. n Suspend an ignition tube containing dilute sulphuric acid in the wash-bottle (Fig.... |
Summarize the following historical passage: | Science
138
You will see in the above Activity that the nature, position and size of
the image formed by a concave mirror depends on the position of the
object in relation to points P, F and C. The image formed is real for some
positions of the object. It is found to be a virtual image for a certain other
position. The image is either magnified, reduced or has the same size,
depending on the position of the object. A summary of these observations
is given for your reference in Table 9.1.
Table 9.1 Image formation by a concave mirror for different positions of the object
Position of the
Position of the
Size of the
Nature of the
object
image
image
image
At infinity
At the focus F
Highly diminished,
Real and inverted
point-sized
Beyond C
Between F and C
Diminished
Real and inverted
At C
At C
Same size
Real and inverted
Between C and F
Beyond C
Enlarged
Real and inverted
At F
At infinity
Highly enlarged
Real and inverted
Between P and F
Behind the mirror
Enlarged
Virtual and erect
9.2.2
Representation of Images Formed by Spherical
Mirrors Using Ray Diagrams
We can also study the formation of images by spherical mirrors by
drawing ray diagrams. Consider an extended object, of finite size, placed
in front of a spherical mirror. Each small portion of the extended object
acts like a point source. An infinite number of rays originate from each
of these points. To construct the ray diagrams, in order to locate the
image of an object, an arbitrarily large number of rays emanating from a
point could be considered. However, it is more convenient to consider
only two rays, for the sake of clarity of the ray diagram. These rays are
so chosen that it is easy to know their directions after reflection from the
mirror.
The intersection of at least two reflected rays give the position of image
of the point object. Any two of the following rays can be considered for
locating the image.
(i)
A ray parallel to the principal
axis, after reflection, will pass
through the principal focus
in case of a concave mirror
or appear to diverge from
the principal focus in
case of a convex mirror.
This is illustrated in Fig.9.3
(a) and (b).
(a)
(b)
Figure
Figure
Figure
Figure
Figure 9.3
9.3
9.3
9.3
9.3
2024-25 | Science 138 You will see in the above Activity that the nature, position and size of the image formed by a concave mirror depends on the position of the object in relation to points P, F and C. The image formed is real for some positions of the object. It... |
Summarize the following historical passage: | Magnetic Effects of Electric Current
199
What happens to the deflection of the compass needle placed at a
given point if the current in the copper wire is changed? To see this, vary
the current in the wire. We find that the deflection in the needle also
changes. In fact, if the current is increased, the deflection also increases.
It indicates that the magnitude of the magnetic field produced at a given
point increases as the current through the wire increases.
What happens to the deflection of the needle if the compass is moved
away from the copper wire but the current through the wire remains the
same? To see this, now place the compass at a farther point from the
conducting wire (say at point Q). What change do you observe? We see
that the deflection in the needle decreases. Thus the magnetic field
produced by a given current in the conductor decreases as the distance
from it increases. From Fig. 12.6, it can be noticed that the concentric
circles representing the magnetic field around a current-carrying straight
wire become larger and larger as we move away from it.
12.2.2 Right-Hand Thumb Rule
A convenient way of finding the direction of magnetic field associated
with a current-carrying conductor is given in Fig. 12.7.
n
Connect the copper wire vertically between the
points X and Y, as shown in Fig. 12.6 (a), in
series with the battery, a plug and key.
n
Sprinkle some iron filings uniformly on the
cardboard. (You may use a salt sprinkler for this
purpose.)
n
Keep the variable of the rheostat at a fixed
position and note the current through the
ammeter.
n
Close the key so that a current flows through
the wire. Ensure that the copper wire placed
between the points X and Y remains vertically
straight.
n
Gently tap the cardboard a few times. Observe
the pattern of the iron filings. You would find
that the iron filings align themselves showing
a pattern of concentric circles around the
copper wire (Fig. 12.6).
n
What do these concentric circles represent?
They represent the magnetic field lines.
n
How can the direction of the magnetic field be
found? Place a compass at a point (say P) over
a circle. Observe the direction of the needle. The
direction of the north pole of the compass
needle would give the direction of the field lines
produced by the electric current through the
straight wire at point P. Show the direction by
an arrow.
n
Does the direction of magnetic field lines get
reversed if the direction of current through the
straight copper wire is reversed? Check it.
Figure 12.6
Figure 12.6
Figure 12.6
Figure 12.6
Figure 12.6
(a) A pattern of concentric circles indicating
the field lines of a magnetic field around a
straight conducting wire. The arrows in the
circles show the direction of the field lines.
(b) A close up of the pattern obtained.
(a)
(b)
Variable
resistance
2024-25 | Magnetic Effects of Electric Current 199 What happens to the deflection of the compass needle placed at a given point if the current in the copper wire is changed? To see this, vary the current in the wire. We find that the deflection in the needle also changes. In fact,... |
Summarize the following historical passage: | Magnetic Effects of Electric Current
203
the direction of force acting on the current-carrying rod gets reversed. It
shows that the direction of the force on the conductor depends upon the
direction of current and the direction of the magnetic field. Experiments
have shown that the displacement of the rod is largest (or the magnitude
of the force is the highest) when the direction of current is at right angles
to the direction of the magnetic field. In such a condition we can use a
simple rule to find the direction of the force on the conductor.
In Activity 12.7, we considered the
direction of the current and that of the magnetic
field perpendicular to each other and found
that the force is perpendicular to both of them.
The three directions can be illustrated through
a simple rule, called Fleming’s left-hand rule.
According to this rule, stretch the thumb,
forefinger and middle finger of your left hand
such that they are mutually perpendicular
(Fig. 12.13). If the first finger points in the
direction of magnetic field and the second
finger in the direction of current, then the
thumb will point in the direction of motion or
the force acting on the conductor.
Devices that use current-carrying conductors and magnetic fields
include electric motor, electric generator, loudspeakers, microphones
and measuring instruments.
Example 12.2
An electron enters a magnetic field at right angles to it, as shown
in Fig. 12.14. The direction of force acting on the electron will be
(a)
to the right.
(b)
to the left.
(c)
out of the page.
(d)
into the page.
Solution
Answer is option (d). The direction of force is perpendicular to the
direction of magnetic field and current as given by Fleming’s left hand
rule. Recall that the direction of current is taken opposite to the direction
of motion of electrons. The force is therefore directed into the page.
Figure 12.13
Figure 12.13
Figure 12.13
Figure 12.13
Figure 12.13
Fleming’s left-hand rule
Figure 12.14
Figure 12.14
Figure 12.14
Figure 12.14
Figure 12.14
Q
U
E
S
T
I
O
N
S
?
1.
Which of the following property of a proton can change while it moves
freely in a magnetic field? (There may be more than one correct answer.)
(a)
mass
(b)
speed
(c)
velocity
(d)
momentum
2024-25 | Magnetic Effects of Electric Current 203 the direction of force acting on the current-carrying rod gets reversed. It shows that the direction of the force on the conductor depends upon the direction of current and the direction of the magnetic field. Experiments have shown that the displacement of the rod... |
Summarize the following historical passage: | Science
150
9.3.3 Refraction by Spherical Lenses
You might have seen watchmakers using a small magnifying glass to
see tiny parts. Have you ever touched the surface of a magnifying glass
with your hand? Is it plane surface or curved? Is it thicker in the middle
or at the edges? The glasses used in spectacles and that by a watchmaker
are examples of lenses. What is a lens? How does it bend light rays? We
shall discuss these in this section.
A transparent material bound by two surfaces, of which one or both
surfaces are spherical, forms a lens. This means
that a lens is bound by at least one spherical
surface. In such lenses, the other surface would
be plane. A lens may have two spherical
surfaces, bulging outwards. Such a lens is called
a double convex lens. It is simply called a convex
lens. It is thicker at the middle as compared to
the edges. Convex lens converges light rays as
shown in Fig. 9.12 (a). Hence convex lenses are
also called converging lenses. Similarly, a double
concave lens is bounded by two spherical
surfaces, curved inwards. It is thicker at the
edges than at the middle. Such lenses diverge
light rays as shown in Fig. 9.12 (b). Such lenses
are also called diverging lenses. A double concave
lens is simply called a concave lens.
A lens, either a convex lens or a concave lens,
has two spherical surfaces. Each of these surfaces
forms a part of a sphere. The centres of these
spheres are called centres of curvature of the lens.
The centre of curvature of a lens is usually
represented by the letter C. Since there are two
centres of curvature, we may represent them as C1 and C2. An imaginary
straight line passing through the two centres of curvature of a lens is
called its principal axis. The central point of a lens is its optical centre. It is
Q
U
E
S
T
I
O
N
S
?
1.
A ray of light travelling in air enters obliquely into water. Does the light
ray bend towards the normal or away from the normal? Why?
2.
Light enters from air to glass having refractive index 1.50. What is the
speed of light in the glass? The speed of light in vacuum is 3 × 108 m s–1.
3.
Find out, from Table 9.3, the medium having highest optical density.
Also find the medium with lowest optical density.
4.
You are given kerosene, turpentine and water. In which of these does
the light travel fastest? Use the information given in Table 9.3.
5.
The refractive index of diamond is 2.42. What is the meaning of this
statement?
(a)
Figure 9.12
Figure 9.12
Figure 9.12
Figure 9.12
Figure 9.12
(a) Converging action of a convex lens, (b) diverging
action of a concave lens
(b)
2024-25 | Science 150 9.3.3 Refraction by Spherical Lenses You might have seen watchmakers using a small magnifying glass to see tiny parts. Have you ever touched the surface of a magnifying glass with your hand? Is it plane surface or curved? Is it thicker in the middle or at the edges?... |
Summarize the following historical passage: | Science
180
Example 11.4
The potential difference between the terminals of an electric heater
is 60 V when it draws a current of 4 A from the source. What current
will the heater draw if the potential difference is increased to 120 V?
Solution
We are given, potential difference V = 60 V, current I = 4 A.
According to Ohm’s law,
60 V
=
= 15
4 A
V
R
I
=
Ω.
When the potential difference is increased to 120 V the current is
given by
current =
120 V
=
= 8 A
15
V
R
Ω
.
The current through the heater becomes 8 A.
Example 11.5
Resistance of a metal wire of length 1 m is 26 Ω at 20°C. If the
diameter of the wire is 0.3 mm, what will be the resistivity of the
metal at that temperature? Using Table 11.2, predict the material
of the wire.
Solution
We are given the resistance R of the wire = 26 Ω, the diameter
d = 0.3 mm = 3 × 10-4 m, and the length l of the wire = 1 m.
Therefore, from Eq. (11.10), the resistivity of the given metallic wire is
ρ
= (RA/l) = (Rπd2/4l )
Substitution of values in this gives
ρ
= 1.84 × 10–6 Ω m
The resistivity of the metal at 20°C is 1.84 × 10–6 Ω m. From
Table 11.2, we see that this is the resistivity of manganese.
Example 11.6
A wire of given material having length l and area of cross-section A
has a resistance of 4 Ω. What would be the resistance of another wire
of the same material having length l/2 and area of cross-section 2A?
Solution
For first wire
R1
ρ
=
l
A
= 4Ω
Now for second wire
R2
ρ
/2
=
2
l
A | Science 180 Example 11.4 The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V? Solution We are given, potential difference V... |
Summarize the following historical passage: | Science
42
We have observed in Activity 3.9 that all metals do not react with
oxygen at the same rate. Different metals show different reactivities
towards oxygen. Metals such as potassium and sodium react so
vigorously that they catch fire if kept in the open. Hence, to protect them
and to prevent accidental fires, they are kept immersed in kerosene oil.
At ordinary temperature, the surfaces of metals such as magnesium,
aluminium, zinc, lead, etc., are covered with a thin layer of oxide. The
protective oxide layer prevents the metal from further oxidation. Iron
does not burn on heating but iron filings burn vigorously when sprinkled
in the flame of the burner. Copper does not burn, but the hot metal is
coated with a black coloured layer of copper(II) oxide. Silver and gold do
not react with oxygen even at high temperatures.
Do You Know?
Anodising is a process of forming a thick oxide layer of aluminium. Aluminium
develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it
resistant to further corrosion. The resistance can be improved further by making the
oxide layer thicker. During anodising, a clean aluminium article is made the anode
and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode
reacts with aluminium to make a thicker protective oxide layer. This oxide layer can
be dyed easily to give aluminium articles an attractive finish.
After performing Activity 3.9, you must have observed that sodium
is the most reactive of the samples of metals taken here. The reaction of
magnesium is less vigorous implying that it is not as reactive as sodium.
But burning in oxygen does not help us to decide about the reactivity of
zinc, iron, copper or lead. Let us see some more reactions to arrive at a
conclusion about the order of reactivity of these metals.
3.2.2 What happens when Metals react with Water?
Activity 3.10
Activity 3.10
Activity 3.10
Activity 3.10
Activity 3.10
CAUTION: This Activity needs the teacher’s assistance.
n
Collect the samples of the same metals as in Activity 3.9.
n
Put small pieces of the samples separately in beakers half-filled
with cold water.
n
Which metals reacted with cold water? Arrange them in the
increasing order of their reactivity with cold water.
n
Did any metal produce fire on water?
n
Does any metal start floating after some time?
n
Put the metals that did not react with cold water in beakers
half-filled with hot water.
n
For the metals that did not react with hot water, arrange the
apparatus as shown in Fig. 3.3 and observe their reaction with steam.
n
Which metals did not react even with steam?
n
Arrange the metals in the decreasing order of reactivity with water.
2024-25 | Science 42 We have observed in Activity 3.9 that all metals do not react with oxygen at the same rate. Different metals show different reactivities towards oxygen. Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and... |
Summarize the following historical passage: | Light – Reflection and Refraction
151
usually represented by the letter O. A ray of light through the optical
centre of a lens passes without suffering any deviation. The effective
diameter of the circular outline of a spherical lens is called its aperture.
We shall confine our discussion in this Chapter to such lenses whose
aperture is much less than its radius of curvature and the two centres of
curvatures are equidistant from the optical centre O. Such lenses are
called thin lenses with small apertures. What happens when parallel rays
of light are incident on a lens? Let us do an Activity to understand this.
Activity 9.11
Activity 9.11
Activity 9.11
Activity 9.11
Activity 9.11
CAUTION: Do not look at the Sun directly or through a lens while
doing this Activity or otherwise. You may damage your eyes if you
do so.
n
Hold a convex lens in your hand. Direct it towards the Sun.
n
Focus the light from the Sun on a sheet of paper. Obtain a sharp
bright image of the Sun.
n
Hold the paper and the lens in the same position for a while. Keep
observing the paper. What happened? Why? Recall your experience
in Activity 9.2.
The paper begins to burn producing smoke. It may even catch fire
after a while. Why does this happen? The light from the Sun constitutes
parallel rays of light. These rays were converged by the lens at the sharp
bright spot formed on the paper. In fact, the bright spot you got on the
paper is a real image of the Sun. The concentration of the sunlight at a
point generated heat. This caused the paper to burn.
Now, we shall consider rays of light parallel to the principal axis of a
lens. What happens when you pass such rays of light through a lens?
This is illustrated for a convex lens in Fig.9.12 (a) and for a concave lens
in Fig.9.12 (b).
Observe Fig.9.12 (a) carefully. Several rays of light parallel to the
principal axis are falling on a convex lens. These rays, after refraction
from the lens, are converging to a point on the principal axis. This point
on the principal axis is called the principal focus of the lens. Let us see
now the action of a concave lens.
Observe Fig.9.12 (b) carefully. Several rays of light parallel to the
principal axis are falling on a concave lens. These rays, after refraction
from the lens, are appearing to diverge from a point on the principal
axis. This point on the principal axis is called the principal focus of the
concave lens.
If you pass parallel rays from the opposite surface of the lens, you
get another principal focus on the opposite side. Letter F is usually used
to represent principal focus. However, a lens has two principal foci. They
are represented by F1 and F2. The distance of the principal focus from
the optical centre of a lens is called its focal length. The letter f is used to
represent the focal length. How can you find the focal length of a convex
lens? Recall the Activity 9.11. In this Activity, the distance between the
position of the lens and the position of the image of the Sun gives the
approximate focal length of the lens.
2024-25 | Light – Reflection and Refraction 151 usually represented by the letter O. A ray of light through the optical centre of a lens passes without suffering any deviation. The effective diameter of the circular outline of a spherical lens is called its aperture. We shall confine our discussion in this... |
Summarize the following historical passage: | Magnetic Effects of
Electric Current
12
CHAPTER
I
n the previous Chapter on ‘Electricity’ we learnt about the heating
effects of electric current. What could be the other effects of electric
current? We know that an electric current-carrying wire behaves like a
magnet. Let us perform the following Activity to reinforce it.
Activity 12.1
Activity 12.1
Activity 12.1
Activity 12.1
Activity 12.1
n
Take a straight thick copper wire and place it
between the points X and Y in an electric circuit,
as shown in Fig. 12.1. The wire XY is kept
perpendicular to the plane of paper.
n
Horizontally place a small compass near to this
copper wire. See the position of its needle.
n
Pass the current through the circuit by
inserting the key into the plug.
n
Observe the change in the position of the
compass needle.
Figure 12.1
Figure 12.1
Figure 12.1
Figure 12.1
Figure 12.1
Compass needle is deflected on passing an electric
current through a metallic conductor
We see that the needle is deflected. What does it mean? It means that
the electric current through the copper wire has produced a magnetic
effect. Thus we can say that electricity and magnetism are linked to each
other. Then, what about the reverse possibility of an electric effect of
moving magnets? In this Chapter we will study magnetic fields and such
electromagnetic effects. We shall also study about electromagnets which
involve the magnetic effect of electric current.
Hans Christian Oersted (1777–1851)
Hans Christian Oersted, one of the leading scientists of the 19th
century, played a crucial role in understanding electromagnetism. In
1820 he accidentally discovered that a compass needle got deflected
when an electric current passed through a metallic wire placed nearby.
Through this observation Oersted showed that electricity and
magnetism were related phenomena. His research later created
technologies such as the radio, television and fiber optics. The unit of
magnetic field strength is named the oersted in his honor.
Resistor
Long straight
conductor
2024-25 | Magnetic Effects of Electric Current 12 CHAPTER I n the previous Chapter on ‘Electricity’ we learnt about the heating effects of electric current. What could be the other effects of electric current? We know that an electric current-carrying wire behaves like a magnet. Let us perform the following Activity to... |
Summarize the following historical passage: | Light – Reflection and Refraction
143
The New Cartesian Sign Convention described above is illustrated in
Fig.9.9 for your reference. These sign conventions are applied to obtain
the mirror formula and solve related numerical problems.
9.2.4 Mirror Formula and Magnification
In a spherical mirror, the distance of the
object from its pole is called the object
distance (u). The distance of the image from
the pole of the mirror is called the image
distance (v). You already know that the
distance of the principal focus from the pole
is called the focal length (f). There is a
relationship between these three quantities
given by the mirror formula which is
expressed as
1
1
1
v
u
f
+
=
(9.1)
This formula is valid in all situations for all
spherical mirrors for all positions of the
object. You must use the New Cartesian Sign
Convention while substituting numerical
values for u, v, f, and R in the mirror formula
for solving problems.
Magnification
Magnification produced by a spherical mirror gives the relative extent to
which the image of an object is magnified with respect to the object size.
It is expressed as the ratio of the height of the image to the height of the
object. It is usually represented by the letter m.
If h is the height of the object and h′ is the height of the image, then
the magnification m produced by a spherical mirror is given by
m =
Height of the image (
)
Height of the object ( )
′
h
h
m =
′
h
h
(9.2)
The magnification m is also related to the object distance (u) and
image distance (v). It can be expressed as:
Magnification (m) =
′ = −
h
h
v
u
(9.3)
You may note that the height of the object is taken to be positive as
the object is usually placed above the principal axis. The height of the
image should be taken as positive for virtual images. However, it is to be
taken as negative for real images. A negative sign in the value of the
magnification indicates that the image is real. A positive sign in the value
of the magnification indicates that the image is virtual.
Figure 9.9
Figure 9.9
Figure 9.9
Figure 9.9
Figure 9.9
The New Cartesian Sign Convention for spherical mirrors
2024-25 | Light – Reflection and Refraction 143 The New Cartesian Sign Convention described above is illustrated in Fig.9.9 for your reference. These sign conventions are applied to obtain the mirror formula and solve related numerical problems. 9.2.4 Mirror Formula and Magnification In a spherical mirror, the distance of the object from... |
Summarize the following historical passage: | Science
164
Think it over
You talk of wondrous things you see,
You say the sun shines bright;
I feel him warm, but how can he
Or make it day or night?
– C. CIBBER
Do you know that our eyes can live even after our death? By donating our eyes after we
die, we can light the life of a blind person.
About 35 million people in the developing world are blind and most of them can be
cured. About 4.5 million people with corneal blindness can be cured through corneal
transplantation of donated eyes. Out of these 4.5 million, 60% are children below the
age of 12. So, if we have got the gift of vision, why not pass it on to somebody who does
not have it? What do we have to keep in mind when eyes have to be donated?
n
Eye donors can belong to any age group or sex. People who use spectacles, or those
operated for cataract, can still donate the eyes. People who are diabetic, have
hypertension, asthma patients and those without communicable diseases can also
donate eyes.
weakening of the ciliary muscles and diminishing flexibility of the
eye lens. Sometimes, a person may suffer from both myopia and
hypermetropia. Such people often require bi-focal lenses. A common
type of bi-focal lenses consists of both concave and convex lenses.
The upper portion consists of a concave lens. It facilitates distant
vision. The lower part is a convex lens. It facilitates near vision.
These days, it is possible to correct the refractive defects with
contact lenses or through surgical interventions.
Q
U
E
S
T
I
O
N
S
?
1.
What is meant by power of accommodation of the eye?
2.
A person with a myopic eye cannot see objects beyond 1.2 m distinctly.
What should be the type of the corrective lens used to restore proper
vision?
3.
What is the far point and near point of the human eye with normal
vision?
4.
A student has difficulty reading the blackboard while sitting in the last
row. What could be the defect the child is suffering from? How can it be
corrected?
2024-25 | Science 164 Think it over You talk of wondrous things you see, You say the sun shines bright; I feel him warm, but how can he Or make it day or night? – C. CIBBER Do you know that our eyes can live even after our death? By donating our... |
Summarize the following historical passage: | Science
88
process breaks up the three-carbon pyruvate molecule to give three
molecules of carbon dioxide. The other product is water. Since this
process takes place in the presence of air (oxygen), it is called aerobic
respiration. The release of energy in this aerobic process is a lot greater
than in the anaerobic process. Sometimes, when there is a lack of oxygen
in our muscle cells, another pathway for the break-down of pyruvate is
taken. Here the pyruvate is converted into lactic acid which is also a
three-carbon molecule. This build-up of lactic acid in our muscles during
sudden activity causes cramps.
Figure 5.8
Figure 5.8
Figure 5.8
Figure 5.8
Figure 5.8 Break-down of glucose by various pathways
The energy released during cellular respiration is immediately used
to synthesise a molecule called ATP which is used to fuel all other
activities in the cell. In these processes, ATP is broken down giving rise
to a fixed amount of energy which can drive the endothermic reactions
taking place in the cell.
ATP
ATP is the energy currency for most cellular processes. The energy released during
the process of respiration is used to make an ATP molecule from ADP and inorganic
phosphate.
Endothermic processes in the cell then use this ATP to drive the reactions. When the
terminal phosphate linkage in ATP is broken using water, the energy equivalent to
30.5 kJ/mol is released.
Think of how a battery can provide energy for many different kinds of uses. It can be
used to obtain mechanical energy, light energy, electrical energy and so on. Similarly,
ATP can be used in the cells for the contraction of muscles, protein synthesis,
conduction of nervous impulses and many other activities.
Since the aerobic respiration pathway depends on oxygen, aerobic
organisms need to ensure that there is sufficient intake of oxygen. We
have seen that plants exchange gases through stomata, and the large
inter-cellular spaces ensure that all cells are in contact with air. Carbon
dioxide and oxygen are exchanged by diffusion here. They can go into
More to Know!
2024-25 | Science 88 process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration. The release of energy in this aerobic process is a lot greater than... |
Summarize the following historical passage: | Science
172
If a net charge Q, flows across any cross-section of a conductor in
time t, then the current I, through the cross-section is
I
Q
t
=
(11.1)
The SI unit of electric charge is coulomb (C), which is equivalent to
the charge contained in nearly 6 × 1018 electrons. (We know that an
electron possesses a negative charge of 1.6 × 10–19 C.) The electric
current is expressed by a unit called ampere (A), named after the
French scientist, Andre-Marie Ampere (1775–1836). One ampere is
constituted by the flow of one coulomb of charge per second, that is,
1 A = 1 C/1 s. Small quantities of current are expressed in milliampere
(1 mA = 10–3 A) or in microampere (1 µA = 10–6 A).
An instrument called ammeter measures electric
current in a circuit. It is always connected in series
in a circuit through which the current is to be
measured. Figure 11.1 shows the schematic
diagram of a typical electric circuit comprising a
cell, an electric bulb, an ammeter and a plug key.
Note that the electric current flows in the circuit
from the positive terminal of the cell to the negative
terminal of the cell through the bulb and ammeter.
Figure 11.1
Figure 11.1
Figure 11.1
Figure 11.1
Figure 11.1
A schematic diagram of an electric circuit
comprising – cell, electric bulb, ammeter and
plug key
Q
U
E
S
T
I
O
N
S
?
Example 11.1
A current of 0.5 A is drawn by a filament of an electric bulb for 10
minutes. Find the amount of electric charge that flows through the
circuit.
Solution
We are given, I = 0.5 A; t = 10 min = 600 s.
From Eq. (11.1), we have
Q
= It
= 0.5 A × 600 s
= 300 C
1.
What does an electric circuit mean?
2.
Define the unit of current.
3.
Calculate the number of electrons constituting one coulomb of charge.
2024-25 | Science 172 If a net charge Q, flows across any cross-section of a conductor in time t, then the current I, through the cross-section is I Q t = (11.1) The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly 6 ×... |
Summarize the following historical passage: | How do Organisms Reproduce?
121
Figure 7.8
Figure 7.8
Figure 7.8
Figure 7.8
Figure 7.8
Germination of pollen on
stigma
The swollen bottom part is the ovary, middle elongated part is the style
and the terminal part which may be sticky is the stigma. The ovary
contains ovules and each ovule has an egg cell. The male germ-cell
produced by pollen grain fuses with the female gamete present in
the ovule. This fusion of the germ-cells or fertilisation gives us the
zygote which is capable of growing into a new plant.
Thus the pollen needs to be transferred from the stamen to the
stigma. If this transfer of pollen occurs in the same flower, it is
referred to as self-pollination. On the other hand, if the pollen is
transferred from one flower to another, it is known as cross-
pollination. This transfer of pollen from one flower to another is
achieved by agents like wind, water or animals.
After the pollen lands on a suitable stigma, it has to reach the
female germ-cells which are in the ovary. For this, a tube grows
out of the pollen grain and travels through the style to reach the
ovary.
After fertilisation, the zygote divides several times to form an
embryo within the ovule. The ovule develops a tough coat and is
gradually converted into a seed. The ovary grows rapidly and ripens
to form a fruit. Meanwhile, the petals, sepals, stamens, style and
stigma may shrivel and fall off. Have you ever observed any flower
part still persisting in the fruit? Try and work out the advantages
of seed-formation for the plant. The seed contains the future plant
or embryo which develops into a seedling under appropriate
conditions. This process is known as germination.
Activity 7.7
Activity 7.7
Activity 7.7
Activity 7.7
Activity 7.7
n
Soak a few seeds of Bengal gram (chana)
and keep them overnight.
n
Drain the excess water and cover the seeds
with a wet cloth and leave them for a day.
Make sure that the seeds do not become dry.
n
Cut open the seeds carefully and observe
the different parts.
n
Compare your observations with the Fig. 7.9
and see if you can identify all the parts.
7.3.3 Reproduction in Human Beings
So far, we have been discussing the variety of modes that different species
use for reproduction. Let us now look at the species that we are most
interested in, namely, humans. Humans use a sexual mode of
reproduction. How does this process work?
Let us begin at an apparently unrelated point. All of us know that
our bodies change as we become older. You have learnt changes that
take place in your body earlier in Class VIII also. We notice that our
height has increased continuously from early age till now. We acquire
teeth, we even lose the old, so-called milk teeth and acquire new ones.
Figure 7.9
Figure 7.9
Figure 7.9
Figure 7.9
Figure 7.9
Germination
2024-25 | How do Organisms Reproduce? 121 Figure 7.8 Figure 7.8 Figure 7.8 Figure 7.8 Figure 7.8 Germination of pollen on stigma The swollen bottom part is the ovary, middle elongated part is the style and the terminal part which may be sticky is the stigma. The ovary contains ovules and each... |
Summarize the following historical passage: | Science
46
?
Q
U
E
S
T
I
O
N
S
1.
Why is sodium kept immersed in kerosene oil?
2.
Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
3.
Samples of four metals A, B, C and D were taken and added to the
following solution one by one. The results obtained have been tabulated
as follows.
3.3 HOW DO MET
3.3 HOW DO MET
3.3 HOW DO MET
3.3 HOW DO MET
3.3 HOW DO METALS AND NON-MET
ALS AND NON-MET
ALS AND NON-MET
ALS AND NON-MET
ALS AND NON-METALS REA
ALS REA
ALS REA
ALS REA
ALS REACT?
CT?
CT?
CT?
CT?
In the above activities, you saw the reactions of metals with a number of
reagents. Why do metals react in this manner? Let us recall what we
learnt about the electronic configuration of elements in Class IX. We
learnt that noble gases, which have a completely filled valence shell, show
little chemical activity. We, therefore, explain the reactivity of elements
as a tendency to attain a completely filled valence shell.
Let us have a look at the electronic configuration of noble gases and
some metals and non-metals.
We can see from Table 3.3 that a sodium atom has one electron in its
outermost shell. If it loses the electron from its M shell then its L shell
now becomes the outermost shell and that has a stable octet. The nucleus
of this atom still has 11 protons but the number of electrons has
become 10, so there is a net positive charge giving us a sodium cation
Na+. On the other hand chlorine has seven electrons in its outermost shell
Use the Table above to answer the following questions about metals
A, B, C and D.
(i)
Which is the most reactive metal?
(ii)
What would you observe if B is added to a solution of Copper(II)
sulphate?
(iii)
Arrange the metals A, B, C and D in the order of decreasing
reactivity.
4.
Which gas is produced when dilute hydrochloric acid is added to a
reactive metal? Write the chemical reaction when iron reacts with dilute
H2SO4.
5.
What would you observe when zinc is added to a solution of iron(II)
sulphate? Write the chemical reaction that takes place.
Metal
Iron(II) sulphate
Copper(II) sulphate
Zinc sulphate
Silver nitrate
A
No reaction
Displacement
B
Displacement
No reaction
C
No reaction
No reaction
No reaction
Displacement
D
No reaction
No reaction
No reaction
No reaction
2024-25 | Science 46 ? Q U E S T I O N S 1. Why is sodium kept immersed in kerosene oil? 2. Write equations for the reactions of (i) iron with steam (ii) calcium and potassium with water 3. Samples of four metals A, B, C and D were taken... |
Summarize the following historical passage: | Life Processes
5
CHAPTER
H
ow do we tell the difference between what is alive and what is not
alive? If we see a dog running, or a cow chewing cud, or a man
shouting loudly on the street, we know that these are living beings. What
if the dog or the cow or the man were asleep? We would still think that
they were alive, but how did we know that? We see them breathing, and
we know that they are alive. What about plants? How do we know that
they are alive? We see them green, some of us will say. But what about
plants that have leaves of colours other than green? They grow over
time, so we know that they are alive, some will say. In other words, we
tend to think of some sort of movement, either growth-related or not, as
common evidence for being alive. But a plant that is not visibly growing is
still alive, and some animals can breathe without visible movement. So
using visible movement as the defining characteristic of life is not enough.
Movements over very small scales will be invisible to the naked eye –
movements of molecules, for example. Is this invisible molecular
movement necessary for life? If we ask this question to professional
biologists, they will say yes. In fact, viruses do not show any molecular
movement in them (until they infect some cell), and that is partly why
there is a controversy about whether they are truly alive or not.
Why are molecular movements needed for life? We have seen in earlier
classes that living organisms are well-organised structures; they can
have tissues, tissues have cells, cells have smaller components in them,
and so on. Because of the effects of the environment, this organised,
ordered nature of living structures is very likely to keep breaking down
over time. If order breaks down, the organism will no longer be alive. So
living creatures must keep repairing and maintaining their structures.
Since all these structures are made up of molecules, they must move
molecules around all the time.
What are the maintenance processes in living organisms?
Let us explore.
5.1 WHA
5.1 WHA
5.1 WHA
5.1 WHA
5.1 WHAT ARE LIFE PROCESSES?
T ARE LIFE PROCESSES?
T ARE LIFE PROCESSES?
T ARE LIFE PROCESSES?
T ARE LIFE PROCESSES?
The maintenance functions of living organisms must go on even when
they are not doing anything particular. Even when we are just sitting in
2024-25 | Life Processes 5 CHAPTER H ow do we tell the difference between what is alive and what is not alive? If we see a dog running, or a cow chewing cud, or a man shouting loudly on the street, we know that these are living beings. What if the dog... |
Summarize the following historical passage: | Science
166
Activity 10.2
Activity 10.2
Activity 10.2
Activity 10.2
Activity 10.2
n
Take a thick sheet of cardboard and make a small hole or narrow
slit in its middle.
n
Allow sunlight to fall on the narrow slit. This gives a narrow beam
of white light.
n
Now, take a glass prism and allow the light from the slit to fall on
one of its faces as shown in Fig. 10.5.
n
Turn the prism slowly until the light that comes out of it appears
on a nearby screen.
n
What do you observe? You will find a beautiful band of colours.
Why does this happen?
Here PE is the incident ray, EF is the refracted ray and FS is the
emergent ray. You may note that a ray of light is entering from air to
glass at the first surface AB. The light ray on refraction has bent towards
the normal. At the second surface AC, the light ray has entered from
glass to air. Hence it has bent away from normal. Compare the angle of
incidence and the angle of refraction at each refracting surface of the
prism. Is this similar to the kind of bending that occurs in a glass slab?
The peculiar shape of the prism makes the emergent ray bend at an
angle to the direction of the incident ray. This angle is called the angle of
deviation. In this case ∠D is the angle of deviation. Mark the angle of
deviation in the above activity and measure it.
10.4 DISPERSION OF WHITE LIGHT BY A GL
10.4 DISPERSION OF WHITE LIGHT BY A GL
10.4 DISPERSION OF WHITE LIGHT BY A GL
10.4 DISPERSION OF WHITE LIGHT BY A GL
10.4 DISPERSION OF WHITE LIGHT BY A GLASS PRISM
ASS PRISM
ASS PRISM
ASS PRISM
ASS PRISM
You must have seen and appreciated the spectacular colours in a rainbow.
How could the white light of the Sun give us various colours of the
rainbow? Before we take up this question, we shall first go back to the
refraction of light through a prism. The inclined refracting surfaces of a
glass prism show exciting phenomenon. Let us find it out through an
activity.
PE – Incident ray
∠i – Angle of incidence
EF – Refracted ray
∠r – Angle of refraction
FS – Emergent ray
∠e – Angle of emergence
∠A – Angle of the prism
∠D – Angle of deviation
Figure 10.4
Figure 10.4
Figure 10.4
Figure 10.4
Figure 10.4 Refraction of light through a triangular glass prism
2024-25 | Science 166 Activity 10.2 Activity 10.2 Activity 10.2 Activity 10.2 Activity 10.2 n Take a thick sheet of cardboard and make a small hole or narrow slit in its middle. n Allow sunlight to fall on the narrow slit. This gives a narrow beam of white light. n Now, take... |
Summarize the following historical passage: | Acids, Bases and Salts
25
2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS?
2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS?
2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS?
2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS?
2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS?
We know how acid-base indicators can be used to distinguish between
an acid and a base. We have also learnt in the previous section about
dilution and decrease in concentration of H+ or OH– ions in solutions.
Can we quantitatively find the amount of these ions present in a solution?
Can we judge how strong a given acid or base is?
We can do this by making use of a universal indicator, which is a
mixture of several indicators. The universal indicator shows different
colours at different concentrations of hydrogen ions in a solution.
A scale for measuring hydrogen ion concentration in a solution, called
pH scale has been developed. The p in pH stands for ‘potenz’ in German,
meaning power. On the pH scale we can measure pH generally from
0 (very acidic) to 14 (very alkaline). pH should be thought of simply as a
number which indicates the acidic or basic nature of a solution. Higher
the hydronium ion concentration, lower is the pH value.
The pH of a neutral solution is 7. Values less than 7 on the pH scale
represent an acidic solution. As the pH value increases from 7 to 14, it
represents an increase in OH– ion concentration in the solution, that is,
increase in the strength of alkali (Fig. 2.6). Generally paper impregnated
with the universal indicator is used for measuring pH.
Q
U
E
S
T
I
O
N
S
?
1.
Why do HCl, HNO3, etc., show acidic characters in aqueous solutions
while solutions of compounds like alcohol and glucose do not show acidic
character?
2.
Why does an aqueous solution of an acid conduct electricity?
3.
Why does dry HCl gas not change the colour of the dry litmus paper?
4.
While diluting an acid, why is it recommended that the acid should be
added to water and not water to the acid?
5.
How is the concentration of hydronium ions (H3O+) affected when a
solution of an acid is diluted?
6.
How is the concentration of hydroxide ions (OH
–) affected when excess
base is dissolved in a solution of sodium hydroxide?
Figure 2.6
Figure 2.6
Figure 2.6
Figure 2.6
Figure 2.6 Variation of pH with the change in concentration of H+(aq) and OH–(aq) ions
2024-25 | Acids, Bases and Salts 25 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? 2.3 HOW STRONG ARE ACID OR BASE SOLUTIONS? We know how acid-base indicators... |
Summarize the following historical passage: | Acids, Bases and Salts
23
The bulb will start glowing in the case of acids, as shown in Fig. 2.3.
But you will observe that glucose and alcohol solutions do not conduct
electricity. Glowing of the bulb indicates that there is a flow of electric
current through the solution. The electric current is carried through the
acidic solution by ions.
Acids contain H+ ion as cation and anion such as Cl– in HCl, NO3
– in
HNO3, SO2–
4
in H2SO4, CH3COO– in CH3COOH. Since the cation present in
acids is H+, this suggests that acids produce hydrogen ions, H+(aq), in
solution, which are responsible for their acidic properties.
Repeat the same Activity using alkalis such as sodium hydroxide, calcium
hydroxide, etc. What can you conclude from the results of this Activity?
2.2.1 What Happens to an Acid or a Base in a Water Solution?
Do acids produce ions only in aqueous solution? Let us test this.
Activity 2.9
Activity 2.9
Activity 2.9
Activity 2.9
Activity 2.9
n
Take about 1g solid NaCl in a clean and
dry test tube and set up the apparatus as
shown in Fig. 2.4.
n
Add some concentrated sulphuric acid to
the test tube.
n
What do you observe? Is there a gas coming
out of the delivery tube?
n
Test the gas evolved successively with dry
and wet blue litmus paper.
n
In which case does the litmus paper change
colour?
n
On the basis of the above Activity, what do
you infer about the acidic character of:
(i)
dry HCl gas
(ii)
HCl solution?
Figure 2.4
Figure 2.4
Figure 2.4
Figure 2.4
Figure 2.4 Preparation of HCl gas
This experiment suggests that hydrogen ions in HCl are produced
in the presence of water. The separation of H+ ion from HCl molecules
cannot occur in the absence of water.
HCl + H2O → H3O+ + Cl–
Hydrogen ions cannot exist alone, but they exist after combining
with water molecules. Thus hydrogen ions must always be shown as
H+(aq) or hydronium ion (H3O+).
H+ + H2O → H3O+
We have seen that acids give H3O+ or H+(aq) ion in water. Let us see
what happens when a base is dissolved in water.
NaOH(s)
H O
2
→
Na+ (aq) + OH– (aq)
Note to teachers: If the climate is very humid, you will have to pass the gas produced
through a guard tube (drying tube) containing calcium chloride to dry the gas.
2024-25 | Acids, Bases and Salts 23 The bulb will start glowing in the case of acids, as shown in Fig. 2.3. But you will observe that glucose and alcohol solutions do not conduct electricity. Glowing of the bulb indicates that there is a flow of electric current through the solution. The... |
Summarize the following historical passage: | Science
194
194
194
194
194
15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected
in parallel to electric mains supply. What current is drawn from the line if the supply
voltage is 220 V?
16. Which uses more energy, a 250 W TV set in 1 hr, or a 1200 W toaster in 10 minutes?
17. An electric heater of resistance 44 Ω draws 5 A from the service mains for 2 hours.
Calculate the rate at which heat is developed in the heater.
18. Explain the following.
(a)
Why is the tungsten used almost exclusively for filament of electric lamps?
(b)
Why are the conductors of electric heating devices, such as bread-toasters
and electric irons, made of an alloy rather than a pure metal?
(c)
Why is the series arrangement not used for domestic circuits?
(d)
How does the resistance of a wire vary with its area of cross-section?
(e)
Why are copper and aluminium wires usually employed for electricity
transmission?
2024-25 | Science 194 194 194 194 194 15. Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V? 16. Which uses more... |
Summarize the following historical passage: | Science
98
5.5.2 Excretion in Plants
Plants use completely different
strategies for excretion than those
of animals. Oxygen itself can be
thought of as a waste product
generated during photosynthesis!
We have discussed earlier how
plants deal with oxygen as well as
CO2. They can get rid of excess water
by transpiration. For other wastes,
plants use the fact that many of
their tissues consist of dead cells,
and that they can even lose some
parts such as leaves. Many plant
waste products are stored in
cellular vacuoles. Waste products
may be stored in leaves that fall off.
Other waste products are stored as
resins and gums, especially in old
xylem. Plants also excrete some
waste substances into the soil
around them.
What you have learnt
n
Movement of various types can be taken as an indication of life.
n
Maintenance of life requires processes like nutrition, respiration, transport of
materials within the body and excretion of waste products.
n
Autotrophic nutrition involves the intake of simple inorganic materials from the
environment and using an external energy source like the Sun to synthesise complex
high-energy organic material.
n
Heterotrophic nutrition involves the intake of complex material prepared by other
organisms.
n
In human beings, the food eaten is broken down by various steps along the
alimentary canal and the digested food is absorbed in the small intestine to be sent
to all cells in the body.
Think it over!
Organ donation
Organ donation is a generous act of donating an
organ to a person who suffers from non-function of
organ(s). Donation of an organ may be done by the
consent of the donor and his/her family. Anyone
regardless of age or gender can become an organ
and tissue donor. Organ transplants can save or
transform the life of a person. Transplantation is
required because recipient’s organ has been
damaged or has failed by disease or injury. In organ
transplantation the organ is surgically removed
from one person (organ donor) and transplanted to
another person (the recipient). Common
transplantations include corneas, kidneys, heart,
liver, pancreas, lungs, intestines and bone marrow.
Most organ and tissue donations occur just after
the donor has died or when the doctor declares a
person brain dead. But some organs such as
kidney, part of a liver, lung, etc., and tissues can be
donated while the donor is alive.
?
Q
U
E
S
T
I
O
N
S
1.
Describe the structure and functioning of nephrons.
2.
What are the methods used by plants to get rid of excretory products?
3.
How is the amount of urine produced regulated?
2024-25 | Science 98 5.5.2 Excretion in Plants Plants use completely different strategies for excretion than those of animals. Oxygen itself can be thought of as a waste product generated during photosynthesis! We have discussed earlier how plants deal with oxygen as well as CO2. They can get rid of excess water... |
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