Conduction is defined as which of the following?

• A. The transfer of heat when two materials are in physical contact
• B. Heat transfer through air
• C. Radiation of heat
• D. Convection in liquids

Answer: (A)

Conduction is the transfer of thermal energy through direct contact between materials, via molecular interactions and, in metals, free electrons, moving energy from regions of higher temperature to lower temperature. That direct contact is what distinguishes conduction from other heat transfer modes. The option describing heat transfer when two materials are in physical contact matches this definition precisely.

Heat transfer through air can occur, but air is a poor conductor and this description fits more broadly with convection or sometimes radiation depending on the situation. Radiation involves energy transfer by electromagnetic waves and does not require contact. Convection in liquids relies on bulk fluid motion to carry heat, not just direct contact between molecules.