Which mechanism transfers heat through electromagnetic waves without needing a medium?

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

Answer: (A)

Heat transfer through electromagnetic waves without a medium is called radiation. Radiation moves energy using oscillating electric and magnetic fields, so it can travel through empty space. This explains how the Sun warms the Earth even though there’s a vacuum in between. Unlike conduction, which needs atoms to collide and pass energy along, or convection, which relies on the bulk motion of a fluid, radiation does not require any material to transfer heat. Evaporation involves energy going into changing a liquid to vapor at a surface, but it’s a phase-change process, not the general mechanism of heat transfer by waves. So radiation best explains heat transfer without needing a medium.