Which mode of heat transfer occurs via electromagnetic waves and does not require a medium?

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

Answer: (A)

The key idea is heat transfer through electromagnetic waves that can travel through empty space. This is radiation. It doesn’t need a medium, so a solid, liquid, or gas isn’t required for the energy to move from a hotter object to a cooler one. Examples include the sun warming the Earth and a hot object radiating infrared energy to its surroundings. In contrast, conduction needs direct contact and molecular interaction to pass energy, convection relies on the bulk movement of a fluid to transfer heat, and evaporation involves a surface phase change with latent heat transfer rather than waves traveling through space.