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#### Heat and Thermodynamics Book Back Questions

11th Standard

Reg.No. :
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Physics

Time : 00:45:00 Hrs
Total Marks : 30
5 x 1 = 5
1. In hot summer aft er a bath, the body’s

(a)

internal energy decreases

(b)

internal energy increases

(c)

heat decreases

(d)

no change in internal energy and heat

2. A hot cup of coff ee is kept on the table. Aft er some time it attains a thermal equilibrium with the surroundings. By considering the air molecules in the room as a thermodynamic system, which of the following is true

(a)

ΔU > 0, Q = 0

(b)

ΔU > 0, W < 0

(c)

ΔU > 0, Q > 0

(d)

ΔU = 0, Q > 0

3. A distant star emits radiation with maximum intensity at 350 nm. The temperature of the star is

(a)

8280 K

(b)

5000K

(c)

7260 K

(d)

9044 K

4. The efficiency of a heat engine working between the freezing point and boiling point of water is

(a)

6.25%

(b)

20%

(c)

26.8%

(d)

12.5%

5. An ideal refrigerator has a freezer at temperature −12°C. The coefficient of performance of the engine is 5. The temperature of the air (to which the heat ejected) is

(a)

50°C

(b)

45.2°C

(c)

40.2°C

(d)

37.5°C

6. 3 x 2 = 6
7. Define specific heat capacity and give its unit.

8. Define molar specific heat capacity.

9. What is a thermal expansion?

10. 3 x 3 = 9
11. Give an example of a quasi-static process.

12. We often have the experience of pumping air into bicycle tyre using hand pump.
Consider the air inside the pump as a thermodynamic system having volume V at atmospheric pressure and room temperature, 27°C. Assume that the nozzle of the tyre is blocked and you push the pump to a volume 1/4 of V. Calculate the final temperature of air in the pump? (For air , since the nozzle is blocked air will not flow into tyre and it can be treated as an adiabatic compression).

13. During a cyclic process, a heat engine absorbs 500 J of heat from a hot reservoir, does work and ejects an amount of heat 300 J into the surroundings (cold reservoir). Calculate the efficiency of the heat engine?

14. 2 x 5 = 10
15. a. ‘A lake has more rain’.
b. ‘A hot cup of coff ee has more heat’. What is wrong in these two statements?

16. Eiffel tower is made up of iron and its height is roughly 300 m. During winter season (January) in France the temperature is 2°C and in hot summer its average temperature 25°C. Calculate the change in height of Eiffel tower between summer and winter. The linear thermal expansion coefficient for iron α = 10 ×10-6 per °C.