Class 8 (Science assignment)

 

Effects and Uses of Heat Energy

Heat energy plays an important role in our daily life. When an object gains heat, its temperature may increase. Heat can also change the state of matter. For example, ice changes into water when heated, and water changes into steam when heated more. Most substances expand when they are heated and contract when they are cooled. Metals are good conductors of heat, so they are used in cooking utensils. Materials like wood and plastic are poor conductors and are used as handles to protect us from heat. Understanding heat energy helps us use energy safely and efficiently.

MCQs

1. When an object gains heat, its temperature usually:
a) Decreases
b) Increases
c) Remains zero
d) Disappears

2. Ice changes into water by:
a) Cooling
b) Freezing
c) Melting
d) Condensation

3. Water changes into steam by:
a) Evaporation
b) Freezing
c) Melting
d) Condensation

4. Most substances when heated:
a) Contract
b) Expand
c) Break always
d) Become cold

5.     Metals are generally:
a) Poor conductors
b) Good conductors
c) Non-conductors
d) Insulators only

6. Cooking utensils are often made of metal because metals:
a) Stop heat
b) Conduct heat well
c) Are soft
d) Produce cold

7. Wood and plastic are used as handles because they:
a) Conduct heat quickly
b) Are good insulators
c) Produce heat
d) Melt easily

8. The change of gas into liquid is called:
a) Melting
b) Freezing
c) Condensation
d) Boiling

9. Heat energy helps us to:
a) Cook food
b) Freeze everything
c) Stop all motion
d) Remove all energy

10. Materials that do not allow heat to pass easily are called:
a) Conductors
b) Insulators
c) Radiators
d) Metals