QCAA Physics Alternative Sequence Heating processes

This describes an idealized, perfectly reversible process with 100% efficiency, which is impossible in reality due to the Second Law of Thermodynamics. It does not define the metric of efficiency itself.

Efficiency is defined as the ratio of useful work output to the total energy input, often expressed mathematically as $\eta = \frac{W_{out}}{Q_{in}}$.

This describes thermal equilibrium, a state where objects are at the same temperature and no net heat flows between them, not efficiency.

This incorrectly mixes concepts of internal energy and heat capacity. Efficiency is specifically a measure of how much input energy is successfully converted into useful work.

Incorrect. A net increase in average kinetic energy means the temperature of the components is increasing, indicating the system is actively heating up rather than being in a stable state of equilibrium.

Correct. Thermal equilibrium occurs when all components of a system reach the same temperature ($T_1 = T_2$), resulting in zero net transfer of thermal energy between them.

Incorrect. While the net exchange of thermal energy decreases as a system approaches equilibrium, true thermal equilibrium is defined by having exactly zero net exchange.

Incorrect. Thermal equilibrium specifically means there is no net flow of thermal energy between components, not an equal exchange between thermal and kinetic energy.