Radiation refers to heat transfer by which means?

• A. Electromagnetic waves
• B. Direct contact
• C. Fluid movement
• D. Evaporation

Answer: (A)

Radiation is heat transfer by electromagnetic waves. This means energy travels as photons and can move through empty space, so a hot object can warm another without touching it or without a surrounding fluid. The rate of radiant heat transfer depends on factors like temperature difference and surface properties (emissivity). Examples include the sun warming the Earth and the warmth you feel from a distant heater through infrared radiation. By comparison, conduction is heat transfer through direct contact, convection involves heat carried by moving fluids, and evaporation is heat loss during a liquid changing to vapor.