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 Page 1


Heat
3
Y
ou know that woollen clothes are
made from animal fibres. You
also know that cotton clothes are
made from plant fibres. We wear woollen
clothes during winters when it is cold
outside. Woollen clothes keep us warm.
We prefer to wear light coloured cotton
clothes when it is hot. These give us a
feeling of coolness. You might have
wondered why particular types of
clothes are suitable for a particular
season.
In winter you feel cold inside the
house. If you come out in the sun, you
feel warm. In summer, you feel hot even
inside the house. How do we know
whether an object is hot or cold? How
do we find out how hot or cold an object
is? In this chapter we shall try to seek
answers to some of these questions.
3.1  HOT AND COLD
In our day-to-day life, we come across a
number of objects. Some of them are hot
We see that some objects are cold
while some are hot. You also know that
some objects are hotter than others
while some are colder than others.  How
do we decide which object is hotter than
the other? We often do it by touching
the objects. But is our sense of touch
reliable? Let us find out.
Activity 3.1
Take three small tubs/containers. Label
them as A, B and C. Put cold water in
container A and hot water in container
Table 3.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream ?
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 3.1   Feeling water in three containers
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 3.1. Mark these
objects as hot or cold.
Do not touch objects which are too
hot. Be careful while handling a
candle flame or a stove.
Make sure that water is not so hot that
you burn your hand
Rationalised 2023-24
Page 2


Heat
3
Y
ou know that woollen clothes are
made from animal fibres. You
also know that cotton clothes are
made from plant fibres. We wear woollen
clothes during winters when it is cold
outside. Woollen clothes keep us warm.
We prefer to wear light coloured cotton
clothes when it is hot. These give us a
feeling of coolness. You might have
wondered why particular types of
clothes are suitable for a particular
season.
In winter you feel cold inside the
house. If you come out in the sun, you
feel warm. In summer, you feel hot even
inside the house. How do we know
whether an object is hot or cold? How
do we find out how hot or cold an object
is? In this chapter we shall try to seek
answers to some of these questions.
3.1  HOT AND COLD
In our day-to-day life, we come across a
number of objects. Some of them are hot
We see that some objects are cold
while some are hot. You also know that
some objects are hotter than others
while some are colder than others.  How
do we decide which object is hotter than
the other? We often do it by touching
the objects. But is our sense of touch
reliable? Let us find out.
Activity 3.1
Take three small tubs/containers. Label
them as A, B and C. Put cold water in
container A and hot water in container
Table 3.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream ?
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 3.1   Feeling water in three containers
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 3.1. Mark these
objects as hot or cold.
Do not touch objects which are too
hot. Be careful while handling a
candle flame or a stove.
Make sure that water is not so hot that
you burn your hand
Rationalised 2023-24
HEAT 25
your hand and examine it carefully. If
you do not have a thermometer, request
a friend to share it with you. A clinical
thermometer looks like the one shown
in Fig. 3.2.
A clinical thermometer consists of a
long, narrow, uniform glass tube. It has
a bulb at one end. This bulb contains
mercury. Outside the bulb, a small
shining thread of mercury can be seen.
If you do not see the mercury thread,
rotate the thermometer a bit till you see
it.  You will also find a scale on the
thermometer. The scale we use is the
celsius scale, indicated by °C.
Boojho’s confusion shows that we
cannot always rely on our sense of touch
to decide whether an object
is hot or cold. Sometimes
it may deceive us.
Then, how do we find
out how hot an object really
is? A reliable measure of the
hotness of an object is its
temperature. Temperature is
measured by a device called
thermometer.
3.2 MEASURING TEMPERATURE
Have you seen a thermometer? Recall
that when you or someone else in your
family had fever, the temperature was
measured by a thermometer. The
thermometer that measures our body
temperature is called a clinical
thermometer. Hold the thermometer in
Fig. 3.2  A clinical thermom-
eter
A clinical thermometer reads
temperature from 35°C to 42°C.
Activity 3.2
Reading a thermometer
Let us learn how to read a thermometer.
First, note the temperature difference
indicated between the two bigger marks.
Also note down the number of divisions
B. Mix some cold and hot water in
container C.  Now dip your left hand in
container A and the right hand in
container B. After keeping the hands in
the two containers for 2–3 minutes, put
both the hands simultaneously in
container C (Fig. 3.1).  Do both the
hands get the same feeling?
Boojho wondered which of the two scales
shown in Fig. 3.2 he should read.  Paheli told
him that India has adopted the celsius scale
and we should read that scale.  The other scale
with the range 94–108 degrees is the
Fahrenheit scale (°F). It was in use earlier.
Boojho says,“My left hand
tells me that the water in mug
C is hot and the right hand
tells me that the same water
is cold.  What should I
conclude?”
Rationalised 2023-24
Page 3


Heat
3
Y
ou know that woollen clothes are
made from animal fibres. You
also know that cotton clothes are
made from plant fibres. We wear woollen
clothes during winters when it is cold
outside. Woollen clothes keep us warm.
We prefer to wear light coloured cotton
clothes when it is hot. These give us a
feeling of coolness. You might have
wondered why particular types of
clothes are suitable for a particular
season.
In winter you feel cold inside the
house. If you come out in the sun, you
feel warm. In summer, you feel hot even
inside the house. How do we know
whether an object is hot or cold? How
do we find out how hot or cold an object
is? In this chapter we shall try to seek
answers to some of these questions.
3.1  HOT AND COLD
In our day-to-day life, we come across a
number of objects. Some of them are hot
We see that some objects are cold
while some are hot. You also know that
some objects are hotter than others
while some are colder than others.  How
do we decide which object is hotter than
the other? We often do it by touching
the objects. But is our sense of touch
reliable? Let us find out.
Activity 3.1
Take three small tubs/containers. Label
them as A, B and C. Put cold water in
container A and hot water in container
Table 3.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream ?
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 3.1   Feeling water in three containers
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 3.1. Mark these
objects as hot or cold.
Do not touch objects which are too
hot. Be careful while handling a
candle flame or a stove.
Make sure that water is not so hot that
you burn your hand
Rationalised 2023-24
HEAT 25
your hand and examine it carefully. If
you do not have a thermometer, request
a friend to share it with you. A clinical
thermometer looks like the one shown
in Fig. 3.2.
A clinical thermometer consists of a
long, narrow, uniform glass tube. It has
a bulb at one end. This bulb contains
mercury. Outside the bulb, a small
shining thread of mercury can be seen.
If you do not see the mercury thread,
rotate the thermometer a bit till you see
it.  You will also find a scale on the
thermometer. The scale we use is the
celsius scale, indicated by °C.
Boojho’s confusion shows that we
cannot always rely on our sense of touch
to decide whether an object
is hot or cold. Sometimes
it may deceive us.
Then, how do we find
out how hot an object really
is? A reliable measure of the
hotness of an object is its
temperature. Temperature is
measured by a device called
thermometer.
3.2 MEASURING TEMPERATURE
Have you seen a thermometer? Recall
that when you or someone else in your
family had fever, the temperature was
measured by a thermometer. The
thermometer that measures our body
temperature is called a clinical
thermometer. Hold the thermometer in
Fig. 3.2  A clinical thermom-
eter
A clinical thermometer reads
temperature from 35°C to 42°C.
Activity 3.2
Reading a thermometer
Let us learn how to read a thermometer.
First, note the temperature difference
indicated between the two bigger marks.
Also note down the number of divisions
B. Mix some cold and hot water in
container C.  Now dip your left hand in
container A and the right hand in
container B. After keeping the hands in
the two containers for 2–3 minutes, put
both the hands simultaneously in
container C (Fig. 3.1).  Do both the
hands get the same feeling?
Boojho wondered which of the two scales
shown in Fig. 3.2 he should read.  Paheli told
him that India has adopted the celsius scale
and we should read that scale.  The other scale
with the range 94–108 degrees is the
Fahrenheit scale (°F). It was in use earlier.
Boojho says,“My left hand
tells me that the water in mug
C is hot and the right hand
tells me that the same water
is cold.  What should I
conclude?”
Rationalised 2023-24
SCIENCE 26
Precautions to be observed while using a clinical thermometer
? Thermometer should be washed before and after use, preferably with an
antiseptic solution.
? Ensure that before use the mercury level is below 35°C.
? Read the thermometer keeping the level of mercury along the line of sight.
(See Fig. 3.3).
? Handle the thermometer with care. If it hits against some hard object, it can
break.
? Don’t hold the thermometer by the bulb while reading it.
(shown by smaller marks) between these
marks.  Suppose the bigger marks read
one degree and there are five divisions
between them.  Then, one small division
can read 
1
0.2 C
5
??
.
Wash the thermometer, preferably
with an antiseptic solution. Hold it
firmly and give it a few jerks. The jerks
will bring the level of mercury down.
Ensure that it falls below 35°C.  Now
place the bulb of the thermometer
Fig. 3.3  Correct method of reading a clinical
thermometer
under your tongue. After one minute,
take the thermometer out and note the
reading.  This is your body temperature.
The temperature should always be
stated with its unit, °C.
What did you record as your body
temperature?
The normal temperature of human
body is 37°C. Note that the temperature
is stated with its unit.
Let us try to assure Paheli that there
is nothing wrong with her.
Activity 3.3
Measure the body temperature of some
of your friends (at least 10) with a
Table 3.2: Body temperature of
some persons
Name Temperature (°C)
Paheli measured her body
temperature. She got worried as
it was not exactly 37°C.
Rationalised 2023-24
Page 4


Heat
3
Y
ou know that woollen clothes are
made from animal fibres. You
also know that cotton clothes are
made from plant fibres. We wear woollen
clothes during winters when it is cold
outside. Woollen clothes keep us warm.
We prefer to wear light coloured cotton
clothes when it is hot. These give us a
feeling of coolness. You might have
wondered why particular types of
clothes are suitable for a particular
season.
In winter you feel cold inside the
house. If you come out in the sun, you
feel warm. In summer, you feel hot even
inside the house. How do we know
whether an object is hot or cold? How
do we find out how hot or cold an object
is? In this chapter we shall try to seek
answers to some of these questions.
3.1  HOT AND COLD
In our day-to-day life, we come across a
number of objects. Some of them are hot
We see that some objects are cold
while some are hot. You also know that
some objects are hotter than others
while some are colder than others.  How
do we decide which object is hotter than
the other? We often do it by touching
the objects. But is our sense of touch
reliable? Let us find out.
Activity 3.1
Take three small tubs/containers. Label
them as A, B and C. Put cold water in
container A and hot water in container
Table 3.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream ?
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 3.1   Feeling water in three containers
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 3.1. Mark these
objects as hot or cold.
Do not touch objects which are too
hot. Be careful while handling a
candle flame or a stove.
Make sure that water is not so hot that
you burn your hand
Rationalised 2023-24
HEAT 25
your hand and examine it carefully. If
you do not have a thermometer, request
a friend to share it with you. A clinical
thermometer looks like the one shown
in Fig. 3.2.
A clinical thermometer consists of a
long, narrow, uniform glass tube. It has
a bulb at one end. This bulb contains
mercury. Outside the bulb, a small
shining thread of mercury can be seen.
If you do not see the mercury thread,
rotate the thermometer a bit till you see
it.  You will also find a scale on the
thermometer. The scale we use is the
celsius scale, indicated by °C.
Boojho’s confusion shows that we
cannot always rely on our sense of touch
to decide whether an object
is hot or cold. Sometimes
it may deceive us.
Then, how do we find
out how hot an object really
is? A reliable measure of the
hotness of an object is its
temperature. Temperature is
measured by a device called
thermometer.
3.2 MEASURING TEMPERATURE
Have you seen a thermometer? Recall
that when you or someone else in your
family had fever, the temperature was
measured by a thermometer. The
thermometer that measures our body
temperature is called a clinical
thermometer. Hold the thermometer in
Fig. 3.2  A clinical thermom-
eter
A clinical thermometer reads
temperature from 35°C to 42°C.
Activity 3.2
Reading a thermometer
Let us learn how to read a thermometer.
First, note the temperature difference
indicated between the two bigger marks.
Also note down the number of divisions
B. Mix some cold and hot water in
container C.  Now dip your left hand in
container A and the right hand in
container B. After keeping the hands in
the two containers for 2–3 minutes, put
both the hands simultaneously in
container C (Fig. 3.1).  Do both the
hands get the same feeling?
Boojho wondered which of the two scales
shown in Fig. 3.2 he should read.  Paheli told
him that India has adopted the celsius scale
and we should read that scale.  The other scale
with the range 94–108 degrees is the
Fahrenheit scale (°F). It was in use earlier.
Boojho says,“My left hand
tells me that the water in mug
C is hot and the right hand
tells me that the same water
is cold.  What should I
conclude?”
Rationalised 2023-24
SCIENCE 26
Precautions to be observed while using a clinical thermometer
? Thermometer should be washed before and after use, preferably with an
antiseptic solution.
? Ensure that before use the mercury level is below 35°C.
? Read the thermometer keeping the level of mercury along the line of sight.
(See Fig. 3.3).
? Handle the thermometer with care. If it hits against some hard object, it can
break.
? Don’t hold the thermometer by the bulb while reading it.
(shown by smaller marks) between these
marks.  Suppose the bigger marks read
one degree and there are five divisions
between them.  Then, one small division
can read 
1
0.2 C
5
??
.
Wash the thermometer, preferably
with an antiseptic solution. Hold it
firmly and give it a few jerks. The jerks
will bring the level of mercury down.
Ensure that it falls below 35°C.  Now
place the bulb of the thermometer
Fig. 3.3  Correct method of reading a clinical
thermometer
under your tongue. After one minute,
take the thermometer out and note the
reading.  This is your body temperature.
The temperature should always be
stated with its unit, °C.
What did you record as your body
temperature?
The normal temperature of human
body is 37°C. Note that the temperature
is stated with its unit.
Let us try to assure Paheli that there
is nothing wrong with her.
Activity 3.3
Measure the body temperature of some
of your friends (at least 10) with a
Table 3.2: Body temperature of
some persons
Name Temperature (°C)
Paheli measured her body
temperature. She got worried as
it was not exactly 37°C.
Rationalised 2023-24
HEAT 27
clinical thermometer. Record your
observations as in Table 3.2.
Is the body temperature of every
person 37°C?
The temperature of every person may
not be 37°C.  It could be slightly higher
or slightly lower.  Actually, what we call
normal temperature is the average body
temperature of a large number of healthy
persons.
The clinical thermometer is designed
to measure the temperature of human
body only.  The temperature of human
body normally does not go below 35
o
C
or above 42
o
C. That is the reason
that this thermometer has the range
35
o
C to 42
o
C.
Different types of thermometers
are used for different purposes.
The maximum and minimum
temperatures of the previous
day, reported in weather
reports, are measured by a
thermometer called the
maximum -minimum
thermometer.
CAUTION
Do not use a clinical thermometer for
measuring the temperature of any
object other than the human body.
Also avoid keeping the thermometer in
the sun or near a flame. It may break.
this thermometer.  Look at it
carefully and note the highest and
the lowest temperature it can
measure. The range of a
laboratory thermometer is
generally from –10°C to 110°C
(Fig. 3.4). Also, as you did in the
case of the clinical thermometer,
find out how much a small
division on this thermometer
reads.  You would need this
information to read the
thermometer correctly.
Let us now learn how this
thermometer is used.
Activity 3.4
Take some tap water in a beaker
or a mug.  Dip the thermometer
in water so that the bulb is
immersed in water but does not
touch the bottom or the sides of
the container. Hold the
thermometer vertically (Fig. 3.5).
Observe the movement of mercury
in the thermometer.  Wait till the
mercury thread becomes steady.
Fig. 3.4  A laboratory thermometer
3.3 LABORATORY THERMOMETER
How do we measure the temperature of
other objects? For this purpose, there
are other thermometers. One such
thermometer is known as the laboratory
thermometer.  The teacher will show you
Boojho got a naughty idea.  He
wanted to measure the temperature
of hot milk using a clinical
thermometer.  Paheli stopped him
from doing so.
Rationalised 2023-24
Page 5


Heat
3
Y
ou know that woollen clothes are
made from animal fibres. You
also know that cotton clothes are
made from plant fibres. We wear woollen
clothes during winters when it is cold
outside. Woollen clothes keep us warm.
We prefer to wear light coloured cotton
clothes when it is hot. These give us a
feeling of coolness. You might have
wondered why particular types of
clothes are suitable for a particular
season.
In winter you feel cold inside the
house. If you come out in the sun, you
feel warm. In summer, you feel hot even
inside the house. How do we know
whether an object is hot or cold? How
do we find out how hot or cold an object
is? In this chapter we shall try to seek
answers to some of these questions.
3.1  HOT AND COLD
In our day-to-day life, we come across a
number of objects. Some of them are hot
We see that some objects are cold
while some are hot. You also know that
some objects are hotter than others
while some are colder than others.  How
do we decide which object is hotter than
the other? We often do it by touching
the objects. But is our sense of touch
reliable? Let us find out.
Activity 3.1
Take three small tubs/containers. Label
them as A, B and C. Put cold water in
container A and hot water in container
Table 3.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream ?
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 3.1   Feeling water in three containers
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 3.1. Mark these
objects as hot or cold.
Do not touch objects which are too
hot. Be careful while handling a
candle flame or a stove.
Make sure that water is not so hot that
you burn your hand
Rationalised 2023-24
HEAT 25
your hand and examine it carefully. If
you do not have a thermometer, request
a friend to share it with you. A clinical
thermometer looks like the one shown
in Fig. 3.2.
A clinical thermometer consists of a
long, narrow, uniform glass tube. It has
a bulb at one end. This bulb contains
mercury. Outside the bulb, a small
shining thread of mercury can be seen.
If you do not see the mercury thread,
rotate the thermometer a bit till you see
it.  You will also find a scale on the
thermometer. The scale we use is the
celsius scale, indicated by °C.
Boojho’s confusion shows that we
cannot always rely on our sense of touch
to decide whether an object
is hot or cold. Sometimes
it may deceive us.
Then, how do we find
out how hot an object really
is? A reliable measure of the
hotness of an object is its
temperature. Temperature is
measured by a device called
thermometer.
3.2 MEASURING TEMPERATURE
Have you seen a thermometer? Recall
that when you or someone else in your
family had fever, the temperature was
measured by a thermometer. The
thermometer that measures our body
temperature is called a clinical
thermometer. Hold the thermometer in
Fig. 3.2  A clinical thermom-
eter
A clinical thermometer reads
temperature from 35°C to 42°C.
Activity 3.2
Reading a thermometer
Let us learn how to read a thermometer.
First, note the temperature difference
indicated between the two bigger marks.
Also note down the number of divisions
B. Mix some cold and hot water in
container C.  Now dip your left hand in
container A and the right hand in
container B. After keeping the hands in
the two containers for 2–3 minutes, put
both the hands simultaneously in
container C (Fig. 3.1).  Do both the
hands get the same feeling?
Boojho wondered which of the two scales
shown in Fig. 3.2 he should read.  Paheli told
him that India has adopted the celsius scale
and we should read that scale.  The other scale
with the range 94–108 degrees is the
Fahrenheit scale (°F). It was in use earlier.
Boojho says,“My left hand
tells me that the water in mug
C is hot and the right hand
tells me that the same water
is cold.  What should I
conclude?”
Rationalised 2023-24
SCIENCE 26
Precautions to be observed while using a clinical thermometer
? Thermometer should be washed before and after use, preferably with an
antiseptic solution.
? Ensure that before use the mercury level is below 35°C.
? Read the thermometer keeping the level of mercury along the line of sight.
(See Fig. 3.3).
? Handle the thermometer with care. If it hits against some hard object, it can
break.
? Don’t hold the thermometer by the bulb while reading it.
(shown by smaller marks) between these
marks.  Suppose the bigger marks read
one degree and there are five divisions
between them.  Then, one small division
can read 
1
0.2 C
5
??
.
Wash the thermometer, preferably
with an antiseptic solution. Hold it
firmly and give it a few jerks. The jerks
will bring the level of mercury down.
Ensure that it falls below 35°C.  Now
place the bulb of the thermometer
Fig. 3.3  Correct method of reading a clinical
thermometer
under your tongue. After one minute,
take the thermometer out and note the
reading.  This is your body temperature.
The temperature should always be
stated with its unit, °C.
What did you record as your body
temperature?
The normal temperature of human
body is 37°C. Note that the temperature
is stated with its unit.
Let us try to assure Paheli that there
is nothing wrong with her.
Activity 3.3
Measure the body temperature of some
of your friends (at least 10) with a
Table 3.2: Body temperature of
some persons
Name Temperature (°C)
Paheli measured her body
temperature. She got worried as
it was not exactly 37°C.
Rationalised 2023-24
HEAT 27
clinical thermometer. Record your
observations as in Table 3.2.
Is the body temperature of every
person 37°C?
The temperature of every person may
not be 37°C.  It could be slightly higher
or slightly lower.  Actually, what we call
normal temperature is the average body
temperature of a large number of healthy
persons.
The clinical thermometer is designed
to measure the temperature of human
body only.  The temperature of human
body normally does not go below 35
o
C
or above 42
o
C. That is the reason
that this thermometer has the range
35
o
C to 42
o
C.
Different types of thermometers
are used for different purposes.
The maximum and minimum
temperatures of the previous
day, reported in weather
reports, are measured by a
thermometer called the
maximum -minimum
thermometer.
CAUTION
Do not use a clinical thermometer for
measuring the temperature of any
object other than the human body.
Also avoid keeping the thermometer in
the sun or near a flame. It may break.
this thermometer.  Look at it
carefully and note the highest and
the lowest temperature it can
measure. The range of a
laboratory thermometer is
generally from –10°C to 110°C
(Fig. 3.4). Also, as you did in the
case of the clinical thermometer,
find out how much a small
division on this thermometer
reads.  You would need this
information to read the
thermometer correctly.
Let us now learn how this
thermometer is used.
Activity 3.4
Take some tap water in a beaker
or a mug.  Dip the thermometer
in water so that the bulb is
immersed in water but does not
touch the bottom or the sides of
the container. Hold the
thermometer vertically (Fig. 3.5).
Observe the movement of mercury
in the thermometer.  Wait till the
mercury thread becomes steady.
Fig. 3.4  A laboratory thermometer
3.3 LABORATORY THERMOMETER
How do we measure the temperature of
other objects? For this purpose, there
are other thermometers. One such
thermometer is known as the laboratory
thermometer.  The teacher will show you
Boojho got a naughty idea.  He
wanted to measure the temperature
of hot milk using a clinical
thermometer.  Paheli stopped him
from doing so.
Rationalised 2023-24
SCIENCE 28
Are there any variations in the
readings? Discuss the possible reasons.
Let us try to answer this question.
Activity 3.5
Take some hot water in a beaker or a
mug.  Dip the thermometer in water.
Wait till the mercury thread becomes
steady and note the temperature.  Now
take out the thermometer from water.
Observe carefully what happens now.
Do you notice that as soon as you take
the thermometer out of water, the level
of mercury begins to fall.  This means
that the temperature must be read while
the thermometer is in water.
You may recall that while taking your
own temperature, you have to take the
thermometer out of your mouth to note
the reading. Can you then use the
laboratory thermometer to measure your
In addition to the precautions to be taken while reading a clinical
thermometer, the laboratory thermometer
? should be kept upright not tilted. (Fig. 3.5)
? bulb should be surrounded from all sides by the substance of which the
temperature is to be measured. The bulb should not touch the surface of the
container.
Fig. 3.5  Measuring temperature of water with a
laboratory thermometer
Boojho now understands why
clinical thermometer cannot be
used to measure high
temperatures. But still wonders
whether a laboratory thermometer
can be used to measure his body
temperature.
Note the reading. This is the temperature
of water at that time.
Compare the temperature of water
recorded by each student in the class.
Boojho wonders why the level
of mercury should change at
all when the bulb of the
thermometer is brought in contact
with another object?
Rationalised 2023-24
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FAQs on NCERT Textbook: Heat - Science & Technology for UPSC CSE

1. What is heat?
Ans. Heat is a form of energy which is transferred from one body to another as a result of a difference in temperature. It flows from a hotter object to a colder one until both objects reach the same temperature.
2. What are the three modes of heat transfer?
Ans. The three modes of heat transfer are Conduction, Convection, and Radiation. Conduction is the transfer of heat through a solid material, Convection is the transfer of heat through liquids and gases, and Radiation is the transfer of heat through electromagnetic waves.
3. What is the difference between temperature and heat?
Ans. Temperature is a measure of the average kinetic energy of the particles in an object while heat is the total kinetic energy of all the particles in an object. Temperature is measured in degrees Celsius or Fahrenheit, while heat is measured in joules or calories.
4. How does insulation work to reduce heat transfer?
Ans. Insulation reduces heat transfer by creating a barrier between the two objects with different temperatures. This barrier slows down the movement of heat energy from one object to another. Good insulators have a low thermal conductivity which means they do not allow heat to pass through easily.
5. What is specific heat capacity?
Ans. Specific heat capacity is the amount of heat energy required to raise the temperature of one unit of mass of a substance by one degree Celsius. It is a measure of how much energy is required to change the temperature of a material. Different substances have different specific heat capacities.
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