🟢 2025
Q1. One mole of an ideal gas expands isothermally at temperature 300 K from volume 1 L to 4 L. Work done by the gas is:
(a) 828 J
(b) 249 J
(c) 415 J
(d) 500 J
Answer: (c)
Solution: W=nRTln(Vf/Vi)=1×8.314×300×ln(4)≈415J
Q2. For an adiabatic process, the relation between pressure and volume is:
(a) PV = constant
(b) P ∝ V
(c) PV^γ = constant
(d) P/V = constant
Answer: (c)
🟢 2024
Q3. A gas absorbs 500 J of heat and does 300 J of work. Change in internal energy:
(a) 200 J
(b) –200 J
(c) 800 J
(d) 150 J
Answer: (a)
Solution: ΔU = Q – W = 500 – 300 = 200 J
Q4. Efficiency of Carnot engine working between 400 K and 300 K:
(a) 25%
(b) 33%
(c) 50%
(d) 75%
Answer: (a)
η = 1 – Tc/Th = 1 – 300/400 = 0.25 → 25%
🟢 2023
Q5. For one mole of monatomic ideal gas, internal energy at temperature 300 K:
(a) 3/2 RT
(b) 5/2 RT
(c) 3 RT
(d) RT
Answer: (a)
Q6. If heat capacity at constant volume Cv = 12.5 J/K, heat capacity at constant pressure Cp = ?
(a) 12.5 J/K
(b) 20.8 J/K
(c) 25 J/K
(d) 10 J/K
Answer: (b)
Cp – Cv = R = 8.314 → Cp = 12.5 + 8.314 ≈ 20.8 J/K
🟢 2022
Q7. Work done in isochoric process is:
(a) zero
(b) maximum
(c) nRT
(d) negative
Answer: (a)
Q8. An ideal gas undergoes cyclic process. Net work done over cycle:
(a) zero
(b) positive
(c) negative
(d) depends
Answer: (b) or (c) depending on direction; for clockwise cycle (expansion → compression), W > 0
🟢 2021
Q9. First law of thermodynamics: ΔU =
(a) Q + W
(b) Q – W
(c) W – Q
(d) Q/W
Answer: (b)
ΔU = heat added – work done by the system
Q10. For adiabatic expansion of ideal gas:
(a) Temperature increases
(b) Temperature decreases
(c) Temperature remains same
(d) Pressure constant
Answer: (b)
🟢 2020
Q11. Efficiency of reversible heat engine depends on:
(a) Nature of working substance
(b) Temperature of reservoirs
(c) Pressure of reservoirs
(d) Volume of gas
Answer: (b)
Q12. Joule-Thomson effect is observed in:
(a) Isothermal process
(b) Adiabatic process
(c) Free expansion
(d) Isochoric process
Answer: (b)
🟢 2019
Q13. Internal energy of ideal gas depends on:
(a) Temperature
(b) Pressure
(c) Volume
(d) Both P and V
Answer: (a)
Q14. A gas does 400 J of work and ΔU = 200 J. Heat supplied:
(a) 600 J
(b) 200 J
(c) 400 J
(d) 100 J
Answer: (a)
Q = ΔU + W = 200 + 400 = 600 J
🟢 2018
Q15. Work done by ideal gas in isothermal expansion from V1 to V2:
(a) nR(T2 – T1)
(b) nRT ln(V2/V1)
(c) zero
(d) nRT(V2 – V1)
Answer: (b)
Q16. Adiabatic index γ = Cp/Cv. For diatomic gas at room temp:
(a) 5/3
(b) 7/5
(c) 1
(d) 4/3
Answer: (b)
🟢 2017
Q17. If Q = 0, process is:
(a) Isothermal
(b) Isochoric
(c) Adiabatic
(d) Isobaric
Answer: (c)
Q18. Heat capacity of monatomic ideal gas at constant volume:
(a) 3R
(b) 3/2 R
(c) 5/2 R
(d) R
Answer: (b)
🟢 2016
Q19. Work done in adiabatic process:
(a) zero
(b) ΔU
(c) –ΔU
(d) depends
Answer: (b)
W = ΔU for adiabatic process
Q20. Which process has maximum work done for same initial & final states:
(a) Isothermal
(b) Adiabatic
(c) Isochoric
(d) Isobaric
Answer: (a)
🟢 2015
Q21. If temperature of gas doubled in isochoric process, pressure:
(a) Doubles
(b) Halves
(c) Same
(d) Quadruples
Answer: (a)
P ∝ T for fixed volume
Q22. Efficiency of Carnot engine working between 500 K and 300 K:
(a) 40%
(b) 60%
(c) 25%
(d) 50%
Answer: (a)
η = 1 – Tc/Th = 1 – 300/500 = 0.4 → 40%
🟢 2014
Q23. Work done by gas in isobaric expansion:
(a) P(Vf – Vi)
(b) zero
(c) nRT ln(Vf/Vi)
(d) ΔU
Answer: (a)
Q24. In free expansion of ideal gas, ΔU = ?
(a) 0
(b) positive
(c) negative
(d) depends
Answer: (a)
No work done, no heat → ΔU = 0
🟢 2013
Q25. First law of thermodynamics is expression of:
(a) Conservation of mass
(b) Conservation of energy
(c) Conservation of momentum
(d) Conservation of charge
Answer: (b)
Q26. For isothermal process of ideal gas, ΔU = ?
(a) nRT
(b) 0
(c) Q – W
(d) nCvΔT
Answer: (b)