NEET Physics: isothermal and adiabatic processes Practice Questions

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).

Correct answer: A — Isothermal process

For a fixed amount of gas expanding, the isothermal process involves heat exchange, while the adiabatic process involves no heat exchange. Since ΔU = Q - W, the adiabatic process (no heat transfer) generally results in a smaller net change in internal energy compared to an isothermal process where heat might be added.

Correct answer: D — Work done

In an adiabatic process, no heat is exchanged (Q=0). According to the First Law of Thermodynamics (ΔU = Q - W), if Q=0, then ΔU = -W. Since W depends on volume change, the change in internal energy is directly related to the work done.

Correct answer: D — Q

For an ideal gas undergoing an isothermal process, ΔU = nRΔT. Since the process is isothermal, ΔT = 0, therefore ΔU = 0. However, if we consider the relationship derived from the First Law, ΔU = Q - W. Since ΔT=0, ΔU=0. (Note: The standard answer for ΔU is 0 because T is constant, but the relationship asked usually points to the definition of internal energy change for an ideal gas.) Let's rephrase this to focus on the First Law application for clarity. Rephrasing the core concept: ΔU = 0 for isothermal process.

Correct answer: D — Isothermal expansion

If the system is heated by an external source, heat transfer occurs (Q>0). If the process is isothermal, ΔT=0. If the process is adiabatic, Q=0. Since heat is involved, an isothermal process is the appropriate description if temperature is constant, though the question focuses on heat input vs. the process type.

Correct answer: C — positive

In an adiabatic expansion, Q=0. Since work is done by the system, the change in internal energy is W = -ΔU. Since W>0 (expansion), ΔU decreases, and W is positive.

Correct answer: D — Adiabatic process

An adiabatic process is defined as a process where no heat is exchanged between the system and its surroundings (Q=0).

Correct answer: A — The process is adiabatic

In an isothermal process, ΔU = 0. Since ΔU = Q - W, it follows that Q = W.

Correct answer: D — the change in volume

For an isothermal process, W = PΔV. Since P is constant (for ideal gas), the work done is directly proportional to the change in volume (ΔV).

Correct answer: C — Zero

A free expansion means no external work is done (W=0) and no heat is exchanged (Q=0). Since ΔU = Q - W, the change in internal energy is zero.

Correct answer: D — Positive

For a reversible isothermal expansion of an ideal gas, the work done by the gas is W = nRT ln(V_f/Vᵢ). Since the volume increases (ΔV > 0) and T is constant, the work done is positive.

Correct answer: B — No heat is exchanged

An adiabatic process is defined as a process where no heat is exchanged between the system and its surroundings, meaning Q=0.

Correct answer: A — Decreases

In an adiabatic process, no heat is exchanged. If the gas expands (work is done by the gas), the internal energy decreases, leading to a decrease in temperature.

Correct answer: A — ΔU = -W

For an adiabatic process, Q=0. According to the First Law of Thermodynamics (ΔU = Q - W), we have ΔU = -W (since Q=0).

Correct answer: D — P V^γ = constant

For an adiabatic process, the relation PV^γ = constant holds, where γ is the adiabatic index.