STD: 7 SUB: GUJARATI (CH: 12)

 

STD: 7 SUB: GUJARATI (CH:13)

 

STD: 7 SUB GUJARATI (CH 10)

 

SCIENCE CHAPTER 4. Heat and Its Transfer

1. Choose the correct option.

a) In solids, heat is mainly transferred by the process of

.

i) conduction

iii) radiation

ii)

iv)

convection none of these

b) Temperature is measured in

.

i) calories

iii) joules

ii)

iv)

degree celsius

all of these

c) The temperature at which a substance changes from a liquid to a gas is called its

.

i) melting point

ii) boiling point

iii) freezing point

iv) none of the above

2. Assertion and Reason type questions:

In the following questions, two statements are given- one labelled Assertion (A)

and the other labelled Reason (R). Read the statements carefully and choose the

correct alternative (A), (B), (C) and (D) as given below.

(A) Both A and R are true and R is correct explanation of the assertion.

(B) Both A and R are true but R is not the correct explanation of the assertion.

(C) A is true but R is false.

(D) A is false but R is true.

a) Assertion: The exteriors of houses are painted in light colours in hot climate.

Reason: Light colour absorbs large amount of radiant heat.

Assertion is true but the Reason is false.

b) Assertion: When an iron rod at 50°C is brought in contact with water at 30°C, heat

flows from the iron rod to water.

Reason: Heat always flows from a body at a higher temperature to a body at a lower

temperature.

Both Assertion and Reason are true and the Reason is a correct explanation of

the Assertion

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b) Heat emitted from a light bulb

3. Identify the type of heat transfer depicted in the following examples.

a) Touching

a hot spoon

Conduction

Radiation

c) Cooling a room using an air conditioner

Convection

4. Answer the following questions in brief.

a) What are the advantages of an alcohol thermometer

over a mercury thermometer?

Alcohol is useful in measuring the lower temperatures as its freezing point is low.

It has another advantage of being less hazardous in comparison to mercury.

b) On a cold winter day, the temperature was 23 degree fahrenheit. What

would this temperature be in degree celsius?

5

9

32 C

F

=

−

) 32

(

9

5

−

= F

C

) 32

23 (

9

5

−

=

C ° − = 5

c) Differentiate between conductors and insulators.

Conductors

Insulators

The materials that allow heat to pass

through them easily are called

conductors of heat

The materials that do not allow the heat

to pass through them easily are called

insulators.

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b) Which paper clip will fall of the metal rod first?

7. Observe the experimental set-up given below and answer the questions that follow.

a) What happens to the rod, when the Bunsen burner is lit?

Heat is transferred to the metal of the rod just above it and thus it becomes hot.

The paper clip closest to the Bunsen burner will fall of the metal rod first.

c) What can you conclude from this experiment?

Heat is transferred from the hottest end to the coldest end of the rod.

8. Fill the word pyramid using the given clues:

e.

d.

c.

b.

a.

i. The mode of transfer of heat that does not require any medium.

ii. The metal used in a clinical thermometer.

iii. The SI unit of heat.

iv. The celestial object that is the main source of heat on planet Earth.

v. The symbol used for the SI unit of temperature.

b) Which paper clip will fall of the metal rod first?

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5

K

4

S

U

N

3

J

O

U

L

E

2

M

E

R

C

U

R

Y

1

R

A

D

I

A

T

I

O

N

9. Higher Order Thinking Skills (HOTS)

Why do shopkeepers selling ice blocks usually cover them with jute sacks?

Jute sacks act as insulating materials. They prevent the heat from the surroundings

to come in contact with the ice blocks. Thus they prevent the ice from melting

rapidly.