NEET Physics: The first law of thermodynamics Practice Questions

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.

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.

Correct answer: A — Adiabatic process

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

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.

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.

Correct answer: D — Increased by the net result of heat input and work output.

According to the First Law (ΔU = Q - W), if heat is supplied (Q>0) and work is done by the system (W>0), the change in internal energy is the difference, which accounts for both energy input and energy output.

Correct answer: B — Change in internal energy of the system.

ΔU represents the change in the internal energy of the system.

Correct answer: C — 300 J

Using the First Law: ΔU = Q - W. Here, Q = +500 J (absorbed) and W = +200 J (work done by the system). ΔU = 500 J - 200 J = 300 J.

Correct answer: D — 350 J

Using the First Law, ΔU = Q - W. Here, Q = +500 J (absorbed) and W = +150 J (done by the system). Therefore, ΔU = 500 - 150 = 350 J.

Correct answer: D — ΔU = Q - W

The First Law of Thermodynamics is mathematically expressed as ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat absorbed by the system, and W is the work done by the system.

Correct answer: C — Negative.

According to the First Law (ΔU = Q - W), if heat is absorbed (Q>0) and work is done by the system (W>0), the change in internal energy will be less than the heat absorbed. If work is done *by* the system, ΔU decreases (or Q-W results in a smaller net change). In this context, if Q is heat *added* to the system and W is work *done* *by* the system, ΔU is Q-W. For simple conceptual understanding, the change in energy depends on the net flow. If work is done *by* the system, internal energy decreases unless heat is also added. A simpler view: Heat added results in an increase in internal energy, adjusted by work done.

Correct answer: A — 300 J

According to the First Law of Thermodynamics, the change in internal energy (ΔU) is equal to the heat supplied to the system (Q) minus the work done by the system (W): ΔU = Q - W. Here, Q = 500 J and W = 200 J. Therefore, ΔU = 500 J - 200 J = 300 J.

Correct answer: C — The initial and final states of the system.

A state function (like internal energy) depends only on the initial and final states of the system, not on the path taken between those states.

Correct answer: A — Positive (work done by the gas).

When a gas expands, it performs work on its surroundings, meaning the system itself does work, hence the work done *by* the system is positive.

Correct answer: D — ΔU = 0

According to the First Law (ΔU = Q - W), if both Q and W are zero, then ΔU = 0 - 0 = 0. This signifies that the internal energy remains unchanged.