# Engineering Physics Questions and Answers – Thermodynamics – 1

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Thermodynamics – 1”.

1. In a thermal process, the pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out the heat of 30J and work of 10J is done on the gas. If the initial internal energy of the gas was 40 J, then the final internal energy will be?
a) 30 J
b) 20 J
c) 60 J
d) 40 J

Explanation: ∆Q=(Uf-Ui)+∆W
30=Uf-40+10
Uf=60J.

2. A system, after passing through different states returns back to its original state, is called ___________
a) Cyclic process
b) Isothermal process
d) Isobaric process

Explanation: A process in which the system after undergoing a series of changes returns to its initial state is called a cyclic process.

3. Which of the following parameters does not characterize the thermodynamic state of matter?
a) Temperature
b) Pressure
c) Work
d) Volume

Explanation: Work is not a state variable. It is a mod of transfer of energy from the system to surrounding or vice versa.

4. Calculate the work done if temperature is changes from 0°C to 200°C at one atmosphere.
a) 100 cal
b) 200 cal
c) 400 cal
d) 800 cal

Explanation: W=P∆V=R∆T
W=2calK-1×200K
W=400cal.

5. Assertion: When a glass of hot milk placed in a room is allowed to cool, its entropy decreases.
Reason: Allowing the hot object to cool does not violate the second law of thermodynamics.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion
c) Assertion is true but the reason is false
d) Both assertion and reason are false

Explanation: Both the assertion and reason are true but the reason is not the correct explanation of the assertion. As the milk cools, its temperature decreases. The decrease in temperature takes the milk to a lesser disorderly state. As the entropy is a measure of disorder, the entropy of the milk decreases.
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6. Which of the following is not a state function?
a) Work done at constant pressure
b) Enthalpy
c) Work done by conservative force
d) Work done by non0conservative force

Explanation: Work done by non-conservative force is not a state of function. The work done will be different along different paths between two given states of the system.

7. The inside and outside temperature of a refrigerator are 273K and 303K respectively. Assuming that refrigerator cycle is reversible, for every joule of work done, the heat delivered to the surrounding will be?
a) 10 J
b) 20 J
c) 30 J
d) 50 J

Explanation: β=Q2/W=T2/(T1-T2 )=273/(303-273)
Q2=273W/30=273/30×1J=9J
Q1=Q2+W=9+1=10J.

8. The door of a domestic refrigerator is kept open while the switch is on. Then the room will ___________
a) Get heated
b) Ger neither heated nor cooled
c) Gets cooled
d) Gets heated first and then cools

Explanation: Temperature of the room will rise because refrigerator takes less heat from the room and rejects more heat.

9. A Carnot engine working between 300 K and 600 K has a work output of 800 J per cycle. The amount of heat energy supplied to the engine from source per cycle is ___________
a) 1200J
b) 1600J
c) 2400J
d) 3200J

Explanation: Ƞ=W/Q1 =1-T2/T1 =1-300/600=1/2
Q1=2W=2×800=1600J.

10. Heat capacity of a substance is infinite. It means ___________
a) Heat is given out
b) Heat is taken out
c) No change in temperature
d) Heat is first given out and then taken out

Explanation: Whatever amount of heat is taken in or given out by a substance of infinite heat capacity, there is no change in its temperature.

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