## Physics ICSE Class 7 Important Questions Chapter 5 Heat

A. Tick (✓) the following questions.

Question 1.
Heat-is a form of energy which we can –
(a) see
(b) feel
(c) both (a) and (b)
(d) none of these
(b) feel

Question 2.
The sun is a source of –
(a) heat
(b) light
(c) sound
(d) both (a) and (b)

Question 3.
We receive heat energy mainly from –
(a) electricity
(c) sun
(c) sun

Question 4.
Plants prepare their food –
(a) of their own
(b) by using heat of the sun
(c) solely by green pigment without sunlight
(d) None of these
(b) by using heat of the sun

Question 5.
We see fumes coming from ice slab due to the fact that –
(a) ice is very hot
(b) ice is somewhat hot
(c) humidity around ice condenses
(d) none of these
(c) humidity around ice condenses

Question 6.
On rubbing our palms, they get heated because heat energy is then available from –
(a) chemical energy spent in rubbing
(b) mechanical energy spent in rubbing
(c) electrical energy spent in rubbing
(d) none of these
(b) mechanical energy spent in rubbing

Question 7.
An electric bulb glows because electrical energy changes into –
(a) light energy first
(b) heat energy first
(c) chemical energy first
(d) none of these
(b) heat energy first

Question 8.
Burning cooking gas cooks food because heat energy is got by way of change of –
(a) chemical energy
(b) light energy
(c) electrical energy
(d) mechanical energy
(a) chemical energy

Question 9.
Heat energy like water flows from –
(a) a cold object to hot object
(b) a cold object to other cold object
(c) a hot object to other hot object
(d) a hot object to cold object
(d) a hot object to cold object

Question 10.
Heat energy is sum of –
(a) potential energy of molecules
(b) kinetic energy of molecules
(c) potential and kinetic energy of molecules
(d) none of these
(c) potential and kinetic energy of molecules

Question 1.
Define heat as energy.
Heat can be defined as a form of energy which causes sensation of warmth or coldness.

Question 2.
Define units of heat energy.
Unit of heat energy is Joule. Commonly used unit of heat is calorie. One calorie is defined as amount of heat energy used to raise the temperature of lg of water by 1°C.

Question 3.
Describe temperature scales: degree Celsius, fahrenheit and kelvin.
Celsius scale :
Total scale between these points is divided into 100 equal parts. Each part or division is called degree
Celsius which is denoted as °C. Ice point of scale is 0°C. Fahrenheit scale : This scale is on the name of the inventor Fahrenheit. In this scale water turns into ice at 32°F. Total scale between these points is divided into 180 equal parts. Each part or division is called degree fahrenheit which is denoted as °F.

Kelvin scale :
Total scale between these points is divided into 100 equal parts. Each part or division is called kelvin which is denoted as K. Ice point of scale is 273 K.

Question 4.
Describe different modes of heat transfer.
Different modes of transfer of heat are :
(a) Conduction : It is a process of transfer of heat from one end to the other end of the object such that heat flows from particle to particle.
(b) Convection : It is a process of heat transfer by way of actual motion of the particles of a medium being heated.
(c) Radiation : It is a process of transfer of heat from hot object to a cold object even in the absence of a medium.

Question 5.
Decide about conductor and insulator of heat in different applications.
If a substance is good conductor of heat, then heat transfer through conduction is easy. In case of insulators, heat transfer by conduction is almost nil.

Question 6.
Describe construction and working of thermos flask.
It is a special flask which does not allow easy transfer of heat by keeping it insulated from the surrounding. It is popularly known as thermos. You might have seen that it is used to keep hot liquid hot and cold liquid cold for a longer duration.
Construction : Thermos flask has a double walled glass bottle. There is no air between the walls. There is vacuum between the walls. Bottle is placed on a cushion like cork kept inside a plastic case. Cork saves the glass bottle from shocks and breakage. Mouth of the flask has a stopper and a cap.

Working : When hot liquid, say tea, is put in the flask, the mouth of the flask is plugged by tightening its cap. Vacuum between the walls of the bottle do not allow transfer of heat by conduction and convection. Silvered walls from inside and outside of the bottle do not allow radiation of heat. Thus, liquid inside the flask can remain at the same temperature for a very long time.

C. Tick (✓) the best choice :

Question 1.
Heat is a form of energy –
(a) which causes sensation of warmth or coldness
(b) due to random motion of molecules
(c) both (a) and (b)
(d) none of these
(c) both (a) and (b)

Question 2.
Unit of heat energy is –
(a) Celsius
(b) fahrenheit
(c) calorie
(d) kelvin
(c) calorie

Question 3.
1 cal =
(a) 2.4 J
(b) 4.2 J
(c) 0.042 J
(d) 24 J
(b) 4.2 J

Question 4.
Normal human body temperature is –
(a) 98.4°C
(b) 37°C
(c) 37°F
(d) 32°C
(b) 37°C

Question 5.
During melting heat is –
(a) dismissed
(b) absorbed
(c) any of (a) or (b)
(d) none of these
(b) absorbed

D. Fill in the blanks :

Question 6.
Change in temperature of a body depends upon and ………….
Change in temperature of a body depends upon nature of its material and amount of heat supplied.

Question 7.
Whenever there is change in state of matter, temperature is ………….
Whenever there is change in state of matter, temperature is same or unchanged.

Question 8.
Water when heated from 0°C to 4°C it ………….
Water when heated from 0°C to 4°C it contracts.

Question 9.
Radiation requires …………. medium to travel.
Radiation requires no medium to travel.

Question 10.
The process of heat transfer by way of actual motion of the particles of medium being heated is called ………..
The process of heat transfer by way of actual motion of the particles of medium being heated is called convection.

E. True or False

Question 11.
Hot air is heavier than cold air.
False.

Question 12.
Conduction currents are set up when gas is heated.
False.

Question 13.
Major part of space is vacuum.
True.

Question 14.
True.

Question 15.
Conduction is a slowest mode of heat transfer.
False.

F. Match the following :

Question 16.

 (A) Conduction (a) molecules actually move (B) Convection (b) Movement of molecules not required (C) Radiation (c) molecules vibrate

 (A) Conduction (c) molecules vibrate (B) Convection (a) molecules actually move (C) Radiation (b) Movement of molecules not required

G Define :

Question 17.
calorie
One calorie is defined as amount of heat energy used to raise the temperature of lg of water by 1°C.

Question 18.
condensation