Does heat transfer require temperature differences?

• A. Yes
• B. No
• C. Only in gases
• D. Not always

Answer: (A)

Heat transfer is driven by a temperature difference—the energy moves from the hotter region to the cooler one until both reach the same temperature. This driving difference works for all ways heat can move: conduction through solids, convection in fluids, and radiation across space. If temperatures are equal, there’s no net heat transfer because the system is in thermal equilibrium. So heat transfer requires a temperature difference. The other ideas—that it can happen without a difference or only in gases—don’t fit how heat transfer actually works, and they ignore the need for a driving temperature gradient.