NATE Air Conditioning and Heat Pumps Practice Exam

Heat transfer that occurs when substances of different temperatures are in contact with each other is called ____.

1. concentration

2. conduction

3. convection

4. radiation

The correct answer is: conduction

Heat transfer that occurs when substances of different temperatures are in contact with each other is known as conduction. This process is fundamental in thermodynamics and occurs at the molecular level. When two bodies at different temperatures come into contact, the molecules of the hotter object, which have more kinetic energy, collide with the molecules of the cooler object, transferring energy. This transfer continues until thermal equilibrium is reached, meaning both objects reach the same temperature. In contrast, concentration refers to the amount of substance in a given volume and does not relate to heat transfer. Convection involves the movement of fluids, where warmer areas of a liquid or gas rise while cooler areas sink, creating a cycle of heat transfer that is not dependent on direct contact. Radiation involves the transfer of heat in the form of electromagnetic waves and does not require a medium for transfer; this is why it can occur even through a vacuum. Understanding these distinctions helps clarify how heat is transferred in different scenarios.