HSSC-1 (Class-11) Solved Physics MCQs; Unit-10: Thermodynamics; (New Book/KPK Text Board, Peshawar) With Verified Answers

HSSC-1 (Class-11) Solved Physics MCQs; Unit-10: Thermodynamics;  (New Book/KPK Text Board, Peshawar) With Verified Answers 

1. Assume we can change the equilibrium state of a system via two different processes. Assume that the initial and the final state are the same. Which of the quantities `\Δ_U`, ΔQ, ΔW, and ΔT must be the same for the two processes?

A. Only ΔQ and ΔW
B. Only ΔU and ΔT
C. Only ΔQ and ΔT
D. Only ΔU and ΔW

... Answer is B. Only ΔU and ΔT
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2. In any process the maximum amount of mechanical energy that can be converted to heat

A. Depends upon the amount of friction
B. Depends upon the intake and exhaust temperature
C. Depends upon whether kinetic or potential energy is involved
D. Is 100%

... Answer is A. Depends upon the amount of friction
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3. In an isothermal change, internal energy

A. Decreases
B. Increases
C. Become zero
D. remains constant

... Answer is D. remains constant
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4. A thermos bottle containing hot coffee is vigorously shaken. Consider coffee as system, then its temperature

A. Increases
B. Decreases below 0°
C. Remains the same
D. Decreases

... Answer is A. Increases
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5. Maximum work can be obtained in tie process called

A. Cyclic
B. Adiabatic
C. Isothermal
D. Isochoric

... Answer is C. Isothermal
----------------------------

6. A heat engine takes in 800 J of heat at 1000 K and exhausts 600 J of heat at 400 K. What the actual efficiency of this engine?

A. 25%
B. 40%
C. 50%
D. 75%

... Answer is A. 25%
Efficiency η% = 1 - `\ frac {QL}{QH}` x 100 = 1 - `\ frac {600}{800}`= 25%

7. If the temperature of the heat source is increased, the efficiency of a Carnot's engine :

A. Increases
B. Decreases
C. Remains constant​
D. First increases and then becomes constant

... Answer is A. Increases
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8. Triple point of water is

A. 273.16°F
B. 273.16°K
C. 273.16°F
D. 273.16°K

... Answer is D. 273.16°K
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9. A real gas can be approximated to an ideal gas at

A. Low density
B. High pressure
C. High density
D. Low temperature

... Answer is A. Low density
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10. If the volume of the gas is to be increased by 4 times, then

A. Temperature and pressure must be double
B. At constant P the temperature must be increased by four times
C. At constant T the pressure must be increased by four times
D. It cannot be increased

... Answer is C. At constant T the pressure must be increased by four times
------------------------

11. In which of the systems listed below is the entropy decreasing?

A. A gas is cooled.
B. A plate is shattered.
C. An egg is scrambled.
D. A drop of dye diffuses in a cup of water.

... Answer is A. A gas is cooled.
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12. If the temperature of the source and sink of a Carnot engine having efficiency η are each decreased by 100K, then the efficiency η :

A. remain constant​
B. First increase then become constant
C. increases.
D. decreases

... Answer is C. increases.
Let T1 = 200 K and T2 = 400 K 👉 Efficiency η% = 1 - `\ frac {T2}{T1}` x 100 = 1 - `\ frac {200 K}{400 K}`= 50% 👉 When the temperature is decrease by 100 K 👉 Efficiency η% = 1 - `\ frac {T2 - 100 K}{T1 - 100 K}` x 100 = 1 - `\ frac {200 K - 100 K}{400 K - 100 K}`= 67%

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