Is a medium required for heat transfer by radiation to occur between surfaces?

• A. Yes
• B. No
• C. Only in a gas
• D. Only in a liquid

Answer: (B)

Radiation transfers heat through electromagnetic waves, which do not need a medium to travel. Surfaces can exchange radiant energy even when nothing is between them, such as in a vacuum, like sunlight traveling from the Sun to the Earth. The presence of a medium only affects how much of that radiation is absorbed or scattered, not whether radiation can occur at all. So no medium is required for heat transfer by radiation to occur between surfaces. The other options imply a medium is necessary or restrict radiation to a gas or liquid, which isn’t true—radiation works with or without a medium.