What is required for heat transfer to occur?

• A. Temperature difference
• B. Pressure difference
• C. Surface area only
• D. Velocity difference

Answer: (A)

Heat transfer happens only when there is a temperature difference between regions or bodies; energy flows from the hotter area to the cooler area until temperatures even out. If temperatures are the same, there is no net heat transfer. The rate at which heat moves can be influenced by surface area (more area allows more energy exchange) and, in moving fluids, by velocity (which enhances convection). Pressure differences don’t by themselves drive heat transfer, and velocity mostly affects how fast it happens rather than whether it occurs at all. Radiation follows the same rule: a temperature difference is required, even though it can occur without a medium.