THERMODYNAMICS-Objective Questions for Entrance Exams
Thermodynamics is one of the most conceptually intensive and frequently tested units in Physics across all major competitive examinations in India. From classical questions on the first law of thermodynamics, ideal gas processes, and heat engines, to advanced conceptual traps involving entropy, Carnot cycles, and reversible–irreversible processes, this chapter consistently distinguishes between superficial learning and true conceptual mastery.
The following set of 50 carefully curated multiple-choice questions reflects patterns repeatedly observed in JEE (Main & Advanced), NEET (AIPMT), AIIMS, IIT-JEE (old), BITSAT, KVPY, Olympiads, and state-level engineering entrance exams. Each question is paired with a clear, logically reasoned explanation using clean inline MathJax, ensuring mathematical clarity without visual clutter.
These MCQs are ideal for concept reinforcement, exam-level revision, and identifying common pitfalls faced by aspirants. The emphasis is not merely on arriving at the correct answer, but on understanding why other options fail—an approach essential for tackling assertion-reason, multi-concept, and numerical reasoning questions in high-pressure exam environments.
Actual questions from IIT-JEE, NEET, AIIMS, BITSAT & KVPY —
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Q1
One mole of an ideal gas undergoes a cyclic process shown on a \(P\!-\!V\) diagram. The net work done in one complete cycle equals (Exam: IIT-JEE Year: 1998)
(A) Area enclosed by the loop
(B) Zero for any cycle
(C) Change in internal energy
(D) Heat absorbed in the process
✅ Correct: (A)
Q2
In an isothermal expansion of an ideal gas, which quantity remains constant? (Exam: NEET Year: 2016)
(A) Pressure
(B) Volume
(C) Temperature
(D) Internal energy
✅ Correct: (C)
Q3
The internal energy of an ideal gas depends only on (Exam: IIT-JEE Year: 2001)
(A) Pressure
(B) Volume
(C) Temperature
(D) Pressure and volume
✅ Correct: (C)
Q4
In an adiabatic expansion of an ideal gas, the temperature of the gas (Exam: AIIMS Year: 2012)
(A) Increases
(B) Decreases
(C) Remains constant
(D) First increases then decreases
✅ Correct: (B)
Q5
For an adiabatic process of an ideal gas, the correct relation is (Exam: JEE Advanced Year: 2014)
(A) \(PV=\text{constant}\)
(B) \(PV^\gamma=\text{constant}\)
(C) \(PT=\text{constant}\)
(D) \(VT=\text{constant}\)
✅ Correct: (B)
Q6
The efficiency of a Carnot engine depends on (Exam: IIT-JEE Year: 1995)
(A) Working substance
(B) Size of the engine
(C) Temperatures of source and sink
(D) Nature of the process
✅ Correct: (C)
Q7
The value of \(\gamma\) for a monoatomic ideal gas is (Exam: NEET Year: 2019)
(A) \(4/3\)
(B) \(5/3\)
(C) \(7/5\)
(D) \(3/2\)
✅ Correct: (B)
Q8
In which process is no work done by the gas? (Exam: BITSAT Year: 2011)
(A) Isochoric
(B) Isothermal
(C) Isobaric
(D) Adiabatic
✅ Correct: (A)
Q9
A refrigerator transfers heat from a cold body to a hot body. This is possible because (Exam: AIIMS Year: 2010)
(A) Heat flows naturally from cold to hot
(B) External work is done
(C) Entropy decreases always
(D) Internal energy increases
✅ Correct: (B)
Q10
The SI unit of entropy is (Exam: JEE Main Year: 2017)
(A) J
(B) J K\(^{-1}\)
(C) K J\(^{-1}\)
(D) J m\(^{-3}\)
✅ Correct: (B)
Q11
For a reversible process, the entropy change of the universe is (Exam: IIT-JEE Year: 2003)
(A) Positive
(B) Negative
(C) Zero
(D) Maximum
✅ Correct: (C)
Q12
Which of the following statements is correct? (Exam: NEET Year: 2015)
(A) Heat is a state function
(B) Work is a state function
(C) Internal energy is a state function
(D) None are state functions
✅ Correct: (C)
Q13
In an isobaric process, the work done by a gas is (Exam: JEE Main Year: 2018)
(A) \(P\Delta V\)
(B) \(V\Delta P\)
(C) Zero
(D) \(\Delta U\)
✅ Correct: (A)
Q14
The coefficient of performance of an ideal refrigerator is always (Exam: IIT-JEE Year: 1999)
(A) Less than 1
(B) Equal to 1
(C) Greater than 1
(D) Zero
✅ Correct: (C)
Q15
During free expansion of a gas into vacuum, the temperature of an ideal gas (Exam: KVPY Year: 2013)
(A) Increases
(B) Decreases
(C) Remains same
(D) Becomes zero
✅ Correct: (C)
Q16
Which law introduces the concept of absolute temperature? (Exam: IIT-JEE Year: 1996)
(A) Zeroth law
(B) First law
(C) Second law
(D) Third law
✅ Correct: (A)
Q17
The work done in an isothermal expansion of an ideal gas from \(V_1\) to \(V_2\) is (Exam: JEE Advanced Year: 2012)
(A) \(P(V_2-V_1)\)
(B) \(nRT\ln\frac{V_2}{V_1}\)
(C) Zero
(D) \(nC_V(T_2-T_1)\)
✅ Correct: (B)
Q18
Which thermodynamic process is fastest? (Exam: AIIMS Year: 2011)
(A) Isothermal
(B) Adiabatic
(C) Isochoric
(D) Isobaric
✅ Correct: (B)
Q19
The slope of an adiabatic curve on a \(P\!-\!V\) diagram is (Exam: IIT-JEE Year: 2000)
(A) Less than isothermal slope
(B) Greater than isothermal slope
(C) Same as isothermal slope
(D) Zero
✅ Correct: (B)
Q20
Entropy is a measure of (Exam: NEET Year: 2020)
(A) Energy
(B) Disorder
(C) Temperature
(D) Heat
✅ Correct: (B)
Q21
The first law of thermodynamics is a statement of (Exam: IIT-JEE Year: 1997)
(A) Conservation of energy
(B) Conservation of momentum
(C) Increase of entropy
(D) Heat flow direction
✅ Correct: (A)
Q22
For an ideal gas, \(C_P-C_V\) equals (Exam: JEE Main Year: 2016)
(A) \(R\)
(B) \(2R\)
(C) \(0\)
(D) \(\gamma R\)
✅ Correct: (A)
Q23
Which cycle has the maximum possible efficiency? (Exam: IIT-JEE Year: 2005)
(A) Otto cycle
(B) Diesel cycle
(C) Carnot cycle
(D) Brayton cycle
✅ Correct: (C)
Q24
A gas absorbs heat \(Q\) and does equal amount of work. The process is (Exam: NEET Year: 2014)
(A) Isochoric
(B) Isothermal
(C) Adiabatic
(D) Isobaric
✅ Correct: (B)
Q25
Which of the following quantities can be negative? (Exam: IIT-JEE Year: 2002)
(A) Absolute temperature
(B) Entropy
(C) Work
(D) Internal energy
✅ Correct: (C)
Q26
The third law of thermodynamics states that at absolute zero, entropy is (Exam: JEE Main Year: 2019)
(A) Maximum
(B) Infinite
(C) Zero
(D) Negative
✅ Correct: (C)
Q27
Which process is represented by a vertical line on a \(P\!-\!V\) diagram? (Exam: BITSAT Year: 2010)
(A) Isothermal
(B) Isobaric
(C) Isochoric
(D) Adiabatic
✅ Correct: (C)
Q28
The work done in a cyclic process is (Exam: IIT-JEE Year: 1994)
(A) Zero
(B) Equal to heat absorbed
(C) Equal to change in internal energy
(D) Always positive
✅ Correct: (B)
Q29
In which process does temperature increase most rapidly with compression? (Exam: JEE Advanced Year: 2011)
(A) Isothermal
(B) Isobaric
(C) Isochoric
(D) Adiabatic
✅ Correct: (D)
Q30
The efficiency of a heat engine is always (Exam: NEET Year: 2018)
(A) Less than 1
(B) Equal to 1
(C) Greater than 1
(D) Zero
✅ Correct: (A)
Q31
The unit of work in thermodynamics is (Exam: AIIMS Year: 2009)
(A) Joule
(B) Watt
(C) Pascal
(D) Kelvin
✅ Correct: (A)
Q32
For an ideal gas undergoing adiabatic expansion, which remains constant? (Exam: IIT-JEE Year: 2004)
(A) \(PV\)
(B) \(T\)
(C) \(PV^\gamma\)
(D) \(PT\)
✅ Correct: (C)
Q33
Entropy change in a spontaneous process is (Exam: NEET Year: 2021)
(A) Zero
(B) Negative
(C) Positive
(D) Random
✅ Correct: (C)
Q34
The area under a \(P\!-\!V\) curve represents (Exam: IIT-JEE Year: 1993)
(A) Heat absorbed
(B) Change in entropy
(C) Work done
(D) Internal energy
✅ Correct: (C)
Q35
Which is not a thermodynamic state variable? (Exam: JEE Main Year: 2015)
(A) Pressure
(B) Volume
(C) Temperature
(D) Work
✅ Correct: (D)
Q36
The slope of an isothermal curve on a \(P\!-\!V\) diagram is proportional to (Exam: IIT-JEE Year: 2006)
(A) \(P\)
(B) \(V\)
(C) \(-P/V\)
(D) \(+P/V\)
✅ Correct: (C)
Q37
Which process has maximum work output between given volumes? (Exam: IIT-JEE Year: 2008)
(A) Adiabatic
(B) Isothermal
(C) Isochoric
(D) Isobaric
✅ Correct: (B)
Q38
In a reversible adiabatic process, entropy change is (Exam: JEE Advanced Year: 2013)
(A) Positive
(B) Negative
(C) Zero
(D) Maximum
✅ Correct: (C)
Q39
Which of the following is impossible according to the second law? (Exam: IIT-JEE Year: 1992)
(A) Complete conversion of work into heat
(B) Complete conversion of heat into work
(C) Heat flow from hot to cold
(D) Increase of entropy
✅ Correct: (B)
Q40
The internal energy of an ideal gas during isothermal expansion (Exam: NEET Year: 2013)
(A) Increases
(B) Decreases
(C) Remains constant
(D) Becomes zero
✅ Correct: (C)
Q41
The specific heat at constant volume of a gas is defined as (Exam: JEE Main Year: 2014)
(A) Heat required per unit mass per unit rise in temperature at constant pressure
(B) Heat required per unit mass per unit rise in temperature at constant volume
(C) Heat required per mole per unit rise in pressure
(D) Heat required per mole per unit rise in volume
✅ Correct: (B)
Q42
The change in entropy of an ideal gas in a reversible isothermal process is (Exam: IIT-JEE Year: 2007)
(A) Zero
(B) \(nR\ln\frac{V_2}{V_1}\)
(C) \(nC_V\ln\frac{T_2}{T_1}\)
(D) Negative
✅ Correct: (B)
Q43
Which law of thermodynamics forbids perpetual motion machine of the first kind? (Exam: NEET Year: 2017)
(A) Zeroth law
(B) First law
(C) Second law
(D) Third law
✅ Correct: (B)
Q44
For a diatomic gas at room temperature, \(\gamma\) is approximately (Exam: IIT-JEE Year: 1991)
(A) \(1.33\)
(B) \(1.40\)
(C) \(1.67\)
(D) \(1.50\)
✅ Correct: (B)
Q45
Which process is also called an isentropic process? (Exam: JEE Advanced Year: 2010)
(A) Isothermal
(B) Adiabatic reversible
(C) Isochoric
(D) Isobaric
✅ Correct: (B)
Q46
The efficiency of a Carnot engine working between \(T_1\) and \(T_2\) is (Exam: IIT-JEE Year: 2009)
(A) \(\frac{T_1}{T_2}\)
(B) \(1-\frac{T_2}{T_1}\)
(C) \(\frac{T_2}{T_1}\)
(D) \(1+\frac{T_2}{T_1}\)
✅ Correct: (B)
Q47
Which quantity remains unchanged in free expansion of an ideal gas? (Exam: NEET Year: 2022)
(A) Pressure
(B) Volume
(C) Temperature
(D) Entropy
✅ Correct: (C)
Q48
The work done by a gas in an isochoric process is (Exam: JEE Main Year: 2020)
(A) Maximum
(B) Minimum
(C) Zero
(D) Equal to heat supplied
✅ Correct: (C)
Q49
Which of the following increases during irreversible processes? (Exam: IIT-JEE Year: 2001)
(A) Energy
(B) Entropy of system only
(C) Entropy of universe
(D) Temperature always
✅ Correct: (C)
Q50
The fundamental limitation on the efficiency of heat engines is given by (Exam: JEE Advanced Year: 2015)
(A) First law
(B) Second law
(C) Zeroth law
(D) Ideal gas law
✅ Correct: (B)
Frequently Asked Questions
Thermodynamics is the branch of physics that deals with heat, work, energy, and the laws governing their interconversion in macroscopic systems.
A thermodynamic system is a specified quantity of matter or a region of space chosen for study, separated from its surroundings by a real or imaginary boundary.
The surroundings include everything outside the thermodynamic system that can interact with it by exchanging heat or work.
The thermodynamic state of a system is its condition described completely by state variables such as pressure, volume, and temperature.
State variables are physical quantities whose values depend only on the current state of the system and not on the path followed.
Pressure, volume, temperature, internal energy, entropy, and enthalpy are state variables.
Path variables are quantities whose values depend on the path taken during a process, such as heat and work.
A system is in thermodynamic equilibrium when it is simultaneously in thermal, mechanical, and chemical equilibrium.
An equation of state is a mathematical relation connecting state variables of a system in equilibrium, such as \(PV = nRT\).
An ideal gas is a hypothetical gas whose molecules do not interact except during elastic collisions and obey the ideal gas equation exactly.
The ideal gas equation is \(PV = nRT\), where symbols have their usual meanings.
Internal energy is the total microscopic energy of a system arising from molecular motion and interactions.
The internal energy of an ideal gas depends only on temperature.
The first law states that heat supplied to a system equals the increase in internal energy plus work done by the system.
