What are the three modes of heat transfer?

• A. Conduction, convection, and radiation
• B. Radiation, conduction, and evaporation
• C. Convection, evaporation, and conduction
• D. Conduction, radiation, and condensation

Answer: (A)

Heat moves in three fundamental ways: conduction, convection, and radiation.

Conduction is energy transfer through direct contact and through the substance itself as molecules and electrons collide and pass kinetic energy along. It’s why a metal spoon gets hot from a pot on the stove—the heat travels from the hotter region to the cooler region by particle interactions and, in metals, by free electrons.

Convection involves the movement of fluid. When a part of the fluid is heated, it becomes less dense and rises, while cooler fluid moves in to take its place, creating a circulating current. This is common in air and water and explains why a heater warms a room through moving air (natural convection) or through a fan (forced convection).

Radiation is heat transfer by electromagnetic waves. It can occur across a vacuum, so you can feel the Sun’s warmth on Earth without touching the Sun. All objects emit infrared radiation, with the amount depending on temperature.

These three are the standard categories for heat transfer. Evaporation and condensation are phase-change processes that involve latent heat transfer, not separate modes of heat transfer, so they aren’t counted as the three modes.