Class - 7 Heat | Subham Sir : Free ICSE, ISC, CBSE Solutions

1. Define heat. Write the SI unit of heat.

Ans. Heat is a form of energy, that is transferred between two different connecting objects with different temperatures. The SI unit is joule (j)

2. Write the relation between calories and joule.

Ans. 1 cal =4.186 j

=4.2 j (approx)

3. Define temperature. Write the SI unit of temperature.

Ans. The temperature is a result of the hotness or coldness of an object. The SI unit is Kelvin (K),

Another unitS are Celsius( C), Fahrenheit (F) and Renkine (R).

4. What is the thermometer? Write the principle of the thermometer.

Ans. Thermometer is a temparature mesurmemt device.

Liquid expansion on heating is the principle of the thermometer.

5. Write the properties of a good thermometer.

Ans. i) Wide range of temparature.

ii) Clear capillary tube.

iii) mercury expands uniformly

6. Write some advantages of mercury in the thermometer.

i) Easily visible for opaque and shiny properties

ii) Uniformly expand ( -39 C to 357 C)

iii) It is not sticky

iv) Good conductor of heat

7. Write the relation between Celsius, Fahrenheit, and Kelvin scale.

Ans.

8. Difference between Centigrade scale and Fahrenheit scale.

Ans:

Centigrade scale	Fahrenheit scale
Lower fixed point is 0 C	Lower fixed point is 32 F
Upper fixed point is 100 C	Upper fixed point is 212 F
100 equal parts	180 equal parts

9. Write all effects of heat.

Ans: i) Change is state

ii) Change in temperature

iii) Change in size ( Expansion and Contraction)

10. How does heat transfer?

Ans: Heat is transferred by conduction, convection, and radiation.

11. Why gap is present between two railway tracks?

Ans: The railway track is made of iron steel so after heating ( sunlight and friction) it is expanded. Rail tracks bend upward due to expansion. To avoid accidents gap is present there.

12. What is the function of a roller under a metal bridge?

Ans: A roller reduces friction and easily carries the road of a metal bridge with expansion.

13. Define bimetallic strip. Write some uses.

Ans: When two different metallic strips join and expand differently it form bimetallic strips.

Uses: i) Fire alarm

ii) Automatic heating device

iii) Refrigerator

14. Define conduction.

Ans: Transfer of heat from high to low temperature through solid substance, this process is called conduction.

15. Define convection.

Ans: Transfer heat through the liquid and gaseous state by the actual movement of molecules this process is called convection.

16. Why ventilator is present top of the room?

Ans: Hot air is lighter and goes up, and out through the ventilator by convection method. Cold air comes inside the room. The ventilator helps to refresh the room.

17. Why is the condenser installed on top of the refrigerator?

Ans: Condenser gives cold air, which is heavier and comes down. So it cools the refrigerator completely.

18. Write the difference between land breeze and sea breeze.

And:

Land Breeze	Sea Breeze
Occur in night time.	Occur in day time.
Air flow land to sea.	Air flow sea to land.
It is usually dry winds.	It contains more moisture.