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NEET Physics: Thermodynamics Practice Questions

15 free multiple-choice questions on Thermodynamics for NEET Physics, each with the correct answer and a step-by-step explanation. Attempt a question, then reveal the solution to check your reasoning.

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  1. Q1. If system A is in thermal equilibrium with system B, and system B is in thermal equilibrium with system C, then what follows according to the Zeroth Law?

    • AA is hotter than C
    • BA is at the same temperature as C
    • CA is at the same temperature as B
    • DA is in thermal equilibrium with C
    Show answer & explanation

    Correct answer: D — A is in thermal equilibrium with C

    The Zeroth Law states that if two bodies are in equilibrium with a third body, they are all in mutual thermal equilibrium, allowing us to define a consistent temperature scale.

  2. Q2. Which term in the First Law of Thermodynamics represents energy transferred across the boundary of a system?

    • APressure
    • BWork
    • CInternal Energy
    • DHeat
    Show answer & explanation

    Correct answer: D — Heat

    Heat (Q) is the transfer of thermal energy across the boundary of a system. Work (W) is the transfer of energy via mechanical means. Internal Energy (ΔU) is the total energy stored within the system.

  3. Q3. Which of the following represents the relationship described by the First Law of Thermodynamics?

    • ATemperature is directly proportional to internal energy.
    • BWork is always negative during an isothermal process.
    • CEnergy can neither be created nor destroyed.
    • DHeat is a vector quantity.
    Show answer & explanation

    Correct answer: C — Energy can neither be created nor destroyed.

    The First Law of Thermodynamics is fundamentally a statement of the conservation of energy, which implies that energy cannot be created or destroyed, only transformed.

  4. Q4. Which of the following physical quantities is the basis for establishing thermal equilibrium according to the Zeroth Law?

    • AHeat energy
    • BWork done
    • CInternal energy
    • DTemperature
    Show answer & explanation

    Correct answer: D — Temperature

    Temperature is the property that determines whether two systems are in thermal equilibrium, as stipulated by the Zeroth Law.

  5. Q5. For a process to be reversible, the change in entropy of the universe must be:

    • Ainfinite
    • Bpositive
    • Czero
    • Dnegative
    Show answer & explanation

    Correct answer: C — zero

    A reversible process occurs when the change in entropy of the universe is exactly zero (as per the condition for reversibility in the context of the Second Law).

  6. Q6. In a process where no heat is exchanged with the surroundings, the change in internal energy of the system is determined solely by the work done. This type of process is known as:

    • AAdiabatic process
    • BIsobaric process
    • CIsothermal process
    • DIsochoric process
    Show answer & explanation

    Correct answer: A — Adiabatic process

    If no heat is exchanged (Q=0), the process is adiabatic. In an adiabatic process, ΔU = -W.

  7. Q7. The Zeroth Law of Thermodynamics is primarily concerned with which concept?

    • AThe internal energy of a system
    • BThermal equilibrium
    • CThe direction of heat transfer
    • DHeat flow between systems
    Show answer & explanation

    Correct answer: B — Thermal equilibrium

    The Zeroth Law establishes the concept of thermal equilibrium. It states that if two systems are in equilibrium with a third system, they are all mutually in equilibrium, which is the foundation for defining temperature.

  8. Q8. When two objects are placed in thermal contact and allowed to reach equilibrium, what defines the temperature of both objects?

    • AThe total heat exchanged between them.
    • BThe point where the net rate of heat transfer becomes zero.
    • CThe rate at which heat flows between them.
    • DThe difference in their internal potential energies.
    Show answer & explanation

    Correct answer: B — The point where the net rate of heat transfer becomes zero.

    Thermal equilibrium is reached when the objects have the same temperature, meaning the net rate of heat transfer between them is zero.

  9. Q9. In a system at thermal equilibrium, the net rate of heat transfer between it and its surroundings is:

    • APositive (heat flows out).
    • BDependent on the mass ratio.
    • CZero.
    • DNegative (heat flows in).
    Show answer & explanation

    Correct answer: C — Zero.

    In thermal equilibrium, there is no net flow of heat between the system and its surroundings; the rate of heat transfer is zero.

  10. Q10. Which of the following statements is the fundamental statement of the Second Law of Thermodynamics?

    • AThe total entropy of an isolated system is either constant or increases.
    • BWork done is always converted entirely into heat in a reversible process.
    • CHeat flows spontaneously from a colder body to a hotter body.
    • DThe total entropy of an isolated system always decreases.
    Show answer & explanation

    Correct answer: A — The total entropy of an isolated system is either constant or increases.

    The Second Law states that for any spontaneous process, the total entropy of the universe (or an isolated system) must increase. If the process is reversible, the entropy remains constant.

  11. Q11. The Zeroth Law is crucial in thermodynamics because it introduces which concept for the first time?

    • AThe concept of thermal balance
    • BEntropy
    • CConservation of energy
    • DThe concept of reversible process
    Show answer & explanation

    Correct answer: A — The concept of thermal balance

    The law is the foundation upon which the concept of temperature, as a state variable, is built.

  12. Q12. Which of the following statements represents the First Law of Thermodynamics?

    • AEnergy can neither be created nor destroyed, only transformed.
    • BThe entropy of an isolated system always increases.
    • CEnergy can be created or destroyed.
    • DHeat flows spontaneously from hot to cold bodies.
    Show answer & explanation

    Correct answer: A — Energy can neither be created nor destroyed, only transformed.

    The First Law of Thermodynamics is based on the principle of energy conservation, stating that energy cannot be created or destroyed, only changed in form.

  13. Q13. If two systems, P and Q, are in thermal equilibrium with each other, and Q is in thermal equilibrium with R, then P and R must be in:

    • Athermal equilibrium
    • Bisolation
    • Cnon-equilibrium
    • Dadiabatic state
    Show answer & explanation

    Correct answer: A — thermal equilibrium

    This is the transitive property derived from the Zeroth Law: if P=Q and Q=R, then P=R (thermal equilibrium).

  14. Q14. For a free expansion of an ideal gas into a vacuum, the work done by the gas is:

    • Adepends on initial pressure
    • Bpositive
    • Czero
    • Dnegative
    Show answer & explanation

    Correct answer: D — negative

    When a gas expands into a vacuum (no external pressure), no work is done by the gas (W = PΔV = 0 since Pₑₓₜ=0).

  15. Q15. If a process occurs at constant volume, the change in internal energy of the system is related to the heat flow by which equation?

    • AΔU = Q - W
    • BΔU = Q
    • CΔU = 0
    • DΔU = Q + W
    Show answer & explanation

    Correct answer: A — ΔU = Q - W

    For a constant volume process, the work done (W) is zero because ΔV = 0 for volume change. Therefore, ΔU = Q - 0, which simplifies to ΔU = Q.

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