Radiation heat transfer can occur without any medium. Which statement is true?

• A. It requires a solid contact
• B. It requires a liquid layer
• C. It can occur in vacuum
• D. It requires a gas

Answer: (C)

Radiation heat transfer is energy carried by electromagnetic waves and does not need a surrounding medium. Any object with temperature above absolute zero emits radiation, and those photons can travel through empty space. In vacuum there are no molecules to enable conduction or convection, yet energy can still move from a hotter body to a cooler one via radiation, as the Sun heats the Earth. That’s why the statement that it can occur in vacuum is true. The other ideas imply a required contact or a specific liquid or gas layer, which isn’t necessary for radiation to take place.