The rate of heat transfer during conduction accelerates when which of the following occurs?

• A. There is a large temperature difference between the heating/cooling agent and the body
• B. The contacting surfaces are identical in material
• C. There is significant air flow between surfaces
• D. The contact area is negligible

Answer: (A)

Heat transfer by conduction speeds up when there is a larger temperature difference across the boundary. The driving force is the temperature gradient: the bigger the difference between the heating/cooling agent and the body, the more energy can move from the hotter to the cooler surface per unit area per unit time. This relationship is captured by the idea that heat transfer by conduction increases with ΔT, multiplied by how well the surfaces conduct and how much contact area exists. So a large temperature difference directly boosts the rate of conduction.

Choosing a larger temperature difference is more influential for conduction than the other factors listed. Merely having identical materials at the interface doesn’t automatically increase the rate, since conduction still depends on the temperature gradient and the contact quality. Air flow between surfaces changes heat transfer mainly through convection rather than conduction at the solid boundary. And a negligible contact area would drastically reduce conduction, not accelerate it.