Which mode can operate without any material medium, including vacuum?

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

Answer: (D)

Heat transfer can occur in three ways, and the one that doesn't require a material medium is radiation. It works by energy moving through electromagnetic waves, which can travel through empty space. This is why the Sun’s warmth reaches Earth across the vacuum of space.

Conduction needs particles to collide and transfer energy, so it requires a solid, liquid, or gas. Convection relies on the movement of a fluid carrying energy, which also depends on having a medium. Evaporation is a phase change from liquid to gas and isn’t a heat-transfer mechanism by itself, though heat can cause it.