How does heat transfer occur?

Heat transfer occurs due to a temperature difference between objects. This fundamental principle underlies all modes of heat transfer—conduction, convection, and radiation. When there is a temperature difference, heat moves from the hotter object to the cooler one until thermal equilibrium is reached, meaning both objects reach the same temperature.

This mechanism is the driving force behind all forms of heat transfer. For example, in conduction, heat flows through materials as faster-moving molecules collide with slower-moving ones, transferring energy. In convection, heat transfers through fluids (liquids and gases) where warmer, less dense regions rise and colder, denser regions sink, establishing a circulation pattern that facilitates energy movement. Although electromagnetic waves, such as infrared radiation, can transfer heat even through a vacuum, the essential requirement is still a temperature difference that prompts the flow of energy. This clarifies that heat transfer is intrinsically linked to differences in thermal energy, making the statement about temperature difference the correct choice.