Which of the following is NOT considered a method of heat transfer?

• A. Diffusion
• B. Conduction
• C. Convection
• D. Radiation

Answer: (A)

The main idea here is the difference between energy transfer and the movement of matter. Heat transfer refers to energy moving from warmer to cooler regions, and it happens mainly in three ways: conduction (energy transfer through interactions inside a solid or between touching surfaces), convection (energy carried by the bulk motion of a fluid), and radiation (energy transferred by electromagnetic waves, even through empty space). Diffusion, by contrast, is about particles spreading out from areas of higher concentration to lower concentration. It’s a mass-transfer process, not a primary mechanism for moving energy from one region to another. While microscopic energy can accompany diffusion, diffusion itself isn’t categorized as a method of heat transfer, which is why it’s not considered a heat transfer mode.