🔥 Thermodynamics – Objective PYQs

Set 1 : Fundamental Objective Questions (JEE Advanced)

Instructions: ✔ Single / Multiple correct ✔ Conceptual + Numerical ✔ Think before applying formulas

Q1️⃣

An ideal gas undergoes free expansion into vacuum. Which of the following are correct?
  • A) Work done = 0
  • B) Heat exchanged = 0
  • C) Temperature decreases
  • D) Internal energy remains same
✔ Correct: A, B, D
Reason: No work, no heat ⇒ ΔU = 0 ⇒ T constant

Q2️⃣

For an isothermal process of an ideal gas:
  • A) ΔU = 0
  • B) Q = W
  • C) Pressure remains constant
  • D) PV = constant
✔ Correct: A, B, D

Q3️⃣

In an adiabatic expansion of an ideal gas:
  • A) Temperature decreases
  • B) Entropy remains constant
  • C) Heat absorbed is zero
  • D) Pressure remains constant
✔ Correct: A, B, C

Q4️⃣

A cyclic process is shown on a P–V diagram. Which is always true?
  • A) Net work = area enclosed
  • B) Net heat absorbed = net work
  • C) Change in internal energy = 0
  • D) Entropy change is zero
✔ Correct: A, B, C

Q5️⃣

For an ideal gas, which relation is always valid?
  • A) Cp − Cv = R
  • B) Cp/Cv = γ
  • C) Internal energy depends only on temperature
  • D) Cv depends on pressure
✔ Correct: A, B, C

Q6️⃣

A heat engine absorbs 800 J and rejects 500 J. Efficiency is:
η = (800 − 500)/800 = 0.375
✔ Answer: 37.5%

Q7️⃣

Which process gives maximum work for fixed initial and final states?
  • A) Free expansion
  • B) Irreversible expansion
  • C) Reversible isothermal expansion
  • D) Isochoric process
✔ Correct: C

Q8️⃣

Entropy change is maximum for:
  • A) Reversible process
  • B) Irreversible process
  • C) Cyclic process
  • D) Adiabatic reversible process
✔ Correct: B

Q9️⃣

In which process does temperature remain constant?
  • A) Isochoric
  • B) Isobaric
  • C) Isothermal
  • D) Adiabatic
✔ Correct: C

Q🔟

For any real heat engine:
  • A) Efficiency can be 100%
  • B) Efficiency < Carnot efficiency
  • C) Efficiency depends on working substance
  • D) Heat rejected cannot be zero
✔ Correct: B, D

✅ Objective Set – Page 1 Completed
➡ Ready for Objective Set – Page 2

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