NCERT Textbook - Heat Class 7 Notes | EduRev

NCERT Textbooks (Class 6 to Class 12)

Created by: Praveen Kumar

Class 7 : NCERT Textbook - Heat Class 7 Notes | EduRev

 Page 1


Heat
4
I
n Chapter 3 you learnt 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.
4.1  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 4.1
Take three large mugs. Label them as
A, B and C.  Put cold water in mug A
and hot water in mug B. Mix some cold
Table 4.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream v
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 4.1   Feeling water in three mugs
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 4.1. 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
© NCERT
not to be republished
Page 2


Heat
4
I
n Chapter 3 you learnt 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.
4.1  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 4.1
Take three large mugs. Label them as
A, B and C.  Put cold water in mug A
and hot water in mug B. Mix some cold
Table 4.1:  Hot and cold objects
Object Cold/Cool Warm/Hot
Ice cream v
Spoon in a
tea cup
Fruit juice
Handle of a
frying pan
Fig. 4.1   Feeling water in three mugs
(A) (B) (C)
and some of them are cold.  Tea is hot
and ice is cold. List some objects you
use commonly in Table 4.1. 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
© NCERT
not to be republished
SCIENCE 36
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. 4.2.
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.
4.2 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. 4.2  A clinical thermometer
A clinical thermometer reads
temperature from 35°C to 42°C.
Activity 4.2
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
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?”
and hot water in mug C.  Now dip your
left hand in mug A and the right hand
in mug B. After keeping the hands in
the two mugs for 2–3 minutes, put both
the hands simultaneously in mug C
(Fig. 4.1).  Do both the hands get the
same feeling?
Boojho wondered which of the two scales
shown in Fig. 4.2 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.
© NCERT
not to be republished
Read More

Up next >

< Previous

Complete Syllabus of Class 7

Dynamic Test

Content Category

Related Searches

mock tests for examination

,

Summary

,

Free

,

practice quizzes

,

Exam

,

video lectures

,

Viva Questions

,

Extra Questions

,

past year papers

,

NCERT Textbook - Heat Class 7 Notes | EduRev

,

Sample Paper

,

MCQs

,

Semester Notes

,

Previous Year Questions with Solutions

,

Objective type Questions

,

pdf

,

NCERT Textbook - Heat Class 7 Notes | EduRev

,

shortcuts and tricks

,

NCERT Textbook - Heat Class 7 Notes | EduRev

,

study material

,

ppt

,

Important questions

;