Class 11 Physics Chapter 11 Thermodynamics – Extra Questions with Answers

Extra practice questions for Class 11 Physics Chapter 11 (Thermodynamics), beyond the textbook. These Class 11 Physics Chapter 11 important questions are handy for last-minute exam practice.

Very Short Answer Questions (1 mark)

Q1. State the zeroth law of thermodynamics.
Ans: If two systems are separately in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

Q2. What is ΔU in an isothermal process?
Ans: Zero, since temperature (and hence internal energy of an ideal gas) does not change.

Q3. What is ΔQ in an adiabatic process?
Ans: Zero, no heat exchange occurs.

Q4. Write the formula for efficiency of a heat engine.
Ans: η=W/Q₁=1−Q₂/Q₁.

Q5. Can the efficiency of any real heat engine be 100%?
Ans: No, by the second law of thermodynamics, no engine can be 100% efficient.

Short Answer Questions (2–3 marks)

Q6. A gas absorbs 500 J of heat and does 200 J of work on its surroundings. Find the change in internal energy.
Ans: ΔU=ΔQ−ΔW=500−200=300 J.

Q7. A Carnot engine operates between 600 K and 300 K. Find its efficiency.
Ans: η=1−T2/T1=1−300/600=0.5=50%.

Q8. A heat engine absorbs 800 J from a hot reservoir and rejects 500 J to a cold reservoir. Find its efficiency.
Ans: η=1−Q2/Q1=1−500/800=0.375=37.5%.

Higher-Order Thinking / Application Questions

Q9. A Carnot engine operating between 500 K and 300 K absorbs 1000 J of heat from the source. Calculate the work done by the engine and the heat rejected to the sink, showing the steps.
Ans: Efficiency η=1−T2/T1=1−300/500=0.4. Work done W=ηQ1=0.4(1000)=400 J. Heat rejected Q2=Q1−W=1000−400=600 J (this can also be verified using Q2/Q1=T2/T1=300/500=0.6, so Q2=0.6×1000=600 J, consistent).

Q10. Explain, using the second law of thermodynamics, why a refrigerator (which moves heat from a colder region to a hotter region) requires external work input to operate, even though the first law alone does not forbid spontaneous heat flow from cold to hot.
Ans: The first law of thermodynamics is simply a statement of energy conservation and does not by itself specify the direction in which heat can flow — it would technically allow heat to spontaneously flow from a cold body to a hot body as long as total energy is conserved. However, the second law of thermodynamics (Clausius statement) explicitly forbids heat from flowing spontaneously from a colder to a hotter body without external work being done on the system. This is why a refrigerator, which removes heat from its cold interior and dumps it into the warmer room, must consume electrical energy (external work) to force this non-spontaneous heat flow to happen — without this work input, the process would violate the second law.

Written by Satish

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