NEET Physics: Heat work and internal energy Practice Questions

Correct answer: B — ΔU = Q - W

The fundamental statement of the First Law of Thermodynamics, which relates heat (Q), work (W), and the change in internal energy (ΔU), is ΔU = Q - W.

Correct answer: A — 70 J

Using the First Law of Thermodynamics, ΔU = Q - W. Given Q = 100 J and W = 30 J, ΔU = 100 J - 30 J = 70 J.

Correct answer: A — ΔU = Q - W

The standard formulation of the First Law is ΔU = Q - W, where Q is heat added to the system and W is work done by the system.

Correct answer: D — Increase

In an adiabatic process, Q=0. According to the First Law (ΔU = Q - W), if Q=0, then ΔU = -W. Since work done *by* the system is positive, the internal energy of the system decreases. However, if the system *does work on* the surroundings (work done by system is positive), the internal energy decreases. (Note: If the question implies work done *on* the system, then ΔU = -W, meaning ΔU decreases.)

Correct answer: C — Internal Energy

Internal Energy (U) is the total energy contained within a system, which is the sum of the kinetic energy of its molecules and their potential energy.

Correct answer: B — First Law of Thermodynamics

The First Law of Thermodynamics (ΔU = Q - W) relates heat, work, and the change in internal energy, establishing the conservation of energy, which underpins the definition of internal energy.

Correct answer: C — Temperature

For an ideal gas, the internal energy (U) is a function solely of the absolute temperature (T).

Correct answer: C — Heat is the change in internal energy only

Heat is energy transferred due to a temperature difference, while Internal Energy is the total energy stored inside the system. They are related but distinct concepts.

Correct answer: D — W = P(V₂ - V₁)

For a process at constant temperature (isothermal), the work done by an expanding gas is W = ∫ P dV. For a constant pressure process (or simply relating work done by expansion), W = P ΔV = P(V₂ - V₁).

Correct answer: B — The heat supplied to the system minus the work done by the system

The First Law of Thermodynamics states that the change in internal energy (ΔU) is equal to the heat supplied to the system (Q) minus the work done by the system (W), i.e., ΔU = Q - W.

Correct answer: B — Adiabatic process

An adiabatic process is one where the system is thermally isolated, meaning no heat is exchanged (Q=0). Although this context usually implies Q=0, the question focuses on the context where the system is isolated, meaning Q=0 and thus ΔU = -W. (Revisiting the constraint: If no work is done, the energy change is due to heat transfer. For an adiabatic process, Q=0 is the defining characteristic, implying the energy change is purely due to work.)

Correct answer: A — The change in internal energy of a system depends on the heat supplied and the work done on or by the system.

The First Law states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by the system (W).

Correct answer: D — ΔU = 0

For an ideal gas, internal energy depends only on temperature. In an isothermal process (constant temperature), the change in internal energy is zero, regardless of the heat exchanged.

Correct answer: C — Zero

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

Correct answer: B — ΔU = Q + W

The First Law of Thermodynamics states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by the system (W); i.e., ΔU = Q - W or ΔU = Q + W depending on the definition of work. For systems where W is work done *by* the system, the standard relation is ΔU = Q - W (where W is work done by the system).