What is thermal equilibrium?

Thermal equilibrium refers to a state in which two or more objects in thermal contact no longer exchange heat energy, because they have reached the same temperature. When two objects are at thermal equilibrium, there is no net heat transfer between them; they are effectively at a uniform temperature. This concept is crucial in thermodynamics, as it underpins the understanding of heat transfer and energy conservation.

The correct answer indicates that both objects maintain the same temperature, which is the defining characteristic of thermal equilibrium. This allows for a stable condition where thermal energy is evenly distributed among the objects in question.

In contrast, other options describe scenarios that do not fit the definition of thermal equilibrium. For instance, the freezing point of a substance is specific to phase changes and does not imply that two objects are in equilibrium. Similarly, when two objects are at different temperatures, they are in a state of thermal imbalance and will continue to exchange heat until equilibrium is achieved. The combustion point of an object refers to a chemical reaction occurring at a certain temperature, which is unrelated to the state of thermal equilibrium.