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Class XI · Physics

Thermodynamics: NEET MCQ practice

84 practice questions on Thermodynamics, each with an explanation. Practise them chapter by chapter in the GyaanLoop app.

84

Practice questions

26

Easy

52

Medium

6

Hard

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What Thermodynamics covers

Topics in the NEET (UG) 2026–27 syllabus for this chapter.

  • Thermal equilibrium, zeroth law of thermodynamics, concept of temperature
  • First law of thermodynamics- heat, work and internal energy
  • Second law of thermodynamics- reversible and irreversible processes

Sample questions on Thermodynamics

Try each one, then open the answer and explanation.

Question 1 · Practice question

Read the assertion and reason carefully to mark the correct option out of the options given below: Assertion : If the temperature of a star is doubled then the rate of loss of heat from it becomes 16 times. Reason : Specific heat varies with temperature.

  1. A.A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
  2. B.B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
  3. C.C. If assertion is true but reason is false.
  4. D.D. If the assertion and reason both are false.
Show answer

Answer: B. B. If both assertion and reason are true but reason is not the correct explanation of the assertion.

The assertion is true because the radiant power from a star follows Stefan–Boltzmann law: P ∝ T⁴, so doubling T increases power 16-fold. The reason 'Specific heat varies with temperature' is a true fact, but it has no connection to the T⁴ law; specific heat is about heat capacity, not radiative emission. Therefore, both are true but the reason doesn't explain the assertion.

Question 2 · Practice question

Read the assertion and reason carefully to mark the correct option out of the options given below: Assertion : Blue star is at high temperature than red star. Reason : Wein's displacement law states that T∝(1/λ m ).

  1. A.If both assertion and reason are true and the reason is the correct explanation of the assertion.
  2. B.If both assertion and reason are true but reason is not the correct explanation of the assertion.
  3. C.If assertion is true but reason is false.
  4. D.If the assertion and reason both are false.
Show answer

Answer: A. If both assertion and reason are true and the reason is the correct explanation of the assertion.

Blue stars have higher surface temperature than red stars, which is true according to stellar classification. Wien's displacement law (T ∝ 1/λₘₐₓ) correctly explains this: a hotter object's peak emission shifts to shorter wavelengths, making a blue star hotter than a red one. Some might wrongly choose (b) if they think the reason is true but not explanatory, but here the reason directly explains the assertion.

Question 3 · Practice question

A Carnot engine takes in 3000kcal of heat from a reservoir at 627 ∘ C and gives it to a sink at 27 ∘ C. The work done by the engine is:

  1. A.8.4 × 10 −6 J
  2. B.8.4 × 10 6 J
  3. C.7.4 × 10 6 J
  4. D.7.4 × 10 −6 J
Show answer

Answer: B. 8.4 × 10 6 J

The Carnot efficiency is 1 - T2/T1, with temperatures in Kelvin: T1 = 627 + 273 = 900 K, T2 = 27 + 273 = 300 K. Efficiency = 1 - 300/900 = 2/3. Work output = efficiency × heat input = (2/3) × (3000 kcal). Converting 3000 kcal to joules using 1 kcal ≈ 4184 J gives ≈ 8.37 × 10⁶ J, closest to option (b). The tempting wrong option (c) might come from forgetting to convert to Kelvin or misplacing the decimal during conversion.

Question 4 · Practice question

Which among the following is not an exact differential?

  1. A.Q(dQ = heat absorbed)
  2. B.U(dU = change in internal energy)
  3. C.S(dS = entropy change)
  4. D.G(dG = Gibbs free energy change)
Show answer

Answer: A. Q(dQ = heat absorbed)

The correct answer is (a) because heat (Q) is not a state function — its value depends on the path taken, and hence dQ is an inexact differential. In contrast, internal energy (U), entropy (S), and Gibbs free energy (G) are state functions; their differentials are exact, meaning they depend only on the initial and final states of the system.

Question 5 · Practice question

In a process the pressure of an ideal gas is proportional to square of the volume of the gas. If the temperature of the gas increases in this process, then work done by this gas:

  1. A.is positive
  2. B.is negative
  3. C.is zero
  4. D.may be positive
Show answer

Answer: A. is positive

Given P ∝ V², we find T ∝ V³ using the ideal gas law. Thus, when temperature increases, volume must increase, and since pressure is always positive, the gas expands doing positive work on the surroundings. Option (d) 'may be positive' is tempting but incorrect here because the relationship forces positive work unequivocally if temperature rises.

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