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NEET Thermodynamics (Physics): 5 practice MCQs with answers

By the PrepMatic team · Updated 9 Oct 2026 · 4 min read

Thermodynamics in Physics is about heat, work and internal energy of a gas, and about the limits on turning heat into work. The five MCQs below cover the first law, a Carnot engine, work in an isobaric process, an isothermal expansion and Mayer's relation. They are at NCERT Class 11 level. The Chemistry chapter with the same name is a different topic, covered on NEET Thermodynamics (Chemistry).

What this chapter covers in the NEET syllabus

Thermodynamics is a separate NMC Physics unit, mapped to the Class 11 NCERT chapter of the same name. The topics are:

• Thermal equilibrium and the zeroth law, and the idea of temperature.
• Heat, internal energy and work, and the first law of thermodynamics.
• Isothermal, adiabatic, isochoric and isobaric processes, and work done in each.
• Specific heat capacities of gases, Cp and Cv, and the relation between them.
• The second law, reversible and irreversible processes, heat engines, refrigerators and the Carnot cycle.

Kinetic theory of gases and properties of solids and liquids (calorimetry, heat transfer) are separate NMC units.

Five practice MCQs on Thermodynamics

Question 1

A Carnot engine works between a source at 400 K and a sink at 300 K. Its efficiency is:

• A. 75%
• B. 33%
• C. 25%
• D. 50%

Question 2

A gas absorbs 500 J of heat and does 200 J of work on its surroundings. The change in its internal energy is:

• A. 700 J
• B. 300 J
• C. 200 J
• D. 500 J

Question 3

A gas at a constant pressure of 1 × 10⁵ Pa expands from 2 litres to 5 litres. The work done by the gas is:

• A. 100 J
• B. 500 J
• C. 700 J
• D. 300 J

Question 4

For an ideal gas expanding isothermally, which statement is correct?

• A. The heat absorbed equals the work done by the gas.
• B. The internal energy of the gas increases.
• C. No heat is exchanged with the surroundings.
• D. The work done by the gas is zero.

Question 5

For one mole of an ideal gas, the difference Cp − Cv is equal to:

• A. 2R
• B. R/2
• C. γR
• D. R

Answers and explanations

1. C. Efficiency of a Carnot engine is 1 − T2/T1 with temperatures in kelvin: 1 − 300/400 = 0.25, or 25%. Using the temperature difference over the sink temperature (100/300) is a common error.
2. B. The first law is ΔU = Q − W. Here Q = +500 J and W = +200 J (done by the gas), so ΔU = 300 J.
3. D. For a constant-pressure process, W = PΔV. The volume change is 3 litres = 3 × 10⁻³ m³, so W = 10⁵ × 3 × 10⁻³ = 300 J. Convert litres to cubic metres before multiplying.
4. A. For an ideal gas the internal energy depends only on temperature. An isothermal process has constant temperature, so ΔU = 0, and the first law gives Q = W. Heat is absorbed and entirely converted into work.
5. D. Mayer's relation for an ideal gas is Cp − Cv = R per mole. The ratio Cp/Cv is γ, a different quantity.

How to prepare Thermodynamics (Physics)

• Fix the sign convention. Use ΔU = Q − W, with W positive when the gas expands and Q positive when heat flows into the gas. Mixing this with the chemistry convention (ΔU = q + w) is a classic source of errors, so keep the two chapters apart in your notes.
• Make a table of the four processes. For each of isothermal, isochoric, isobaric and adiabatic, write the condition, the relation between P, V and T, the work done and what Q and ΔU are. Adiabatic means Q = 0, so W = −ΔU. For an ideal gas in a reversible adiabatic change, P times V raised to the power γ stays constant.
• Use P-V diagrams. Work done is the area under the curve, and a cycle's net work is the enclosed area. Practise reading the direction of a loop: clockwise means net work done by the gas.
• Know engine formulas. Efficiency is W/Q1 = 1 − Q2/Q1, and for a Carnot engine it equals 1 − T2/T1. No engine can reach 100% efficiency.
• Check units. Pressure in pascal and volume in cubic metres give work in joules.

Revise the process table daily for a week, and solve one P-V diagram problem a day. The NEET Physics preparation guide has the wider plan, and the NEET syllabus lists every unit.

Take a full Thermodynamics (Physics) test on PrepMatic

For a longer Physics block, you can build a custom mock on PrepMatic by choosing the subject, the number of questions, the duration and the difficulty. A standard topic test is about 15 questions in 30 minutes. Both use NEET's negative marking, and the practice hub lists related chapters.

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