Which term describes heat transfer through a material in contact with each other?

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

Answer: (A)

Conduction is the transfer of heat through a substance that is in direct contact with another, because energy passes from molecule to molecule as they collide and vibrate. In solids, neighboring particles share energy, and in metals especially, free electrons move swiftly and transfer energy quickly from the hotter part to the cooler part. This is why a metal rod heats up along its length when one end is heated.

Convection, by contrast, requires the movement of a fluid; heat is carried by the bulk motion of the fluid itself rather than through contact between solid particles. Radiation is heat transfer via electromagnetic waves and can occur without any contact between materials. Evaporation relates to a phase change at a liquid’s surface and is not the mechanism for heat transfer between two solid materials in contact.

So when heat moves through materials that are touching, conduction is the right term.