Which statement about heat transfer is true?

Which statement about heat transfer is true?

• A. Heat can be transferred by conduction only
• B. Conduction is the only method that can occur in a vacuum
• C. Heat transfer occurs only in solids
• D. Radiation does not require a medium

Answer: (D)

Heat can move in three ways, and the one that doesn’t need any material to travel through is radiation. Radiation transfers energy through electromagnetic waves, so it can heat objects even across empty space. This is why the Sun can warm the Earth through the vacuum of space and why you feel warmth from a hot stove without touching it—the heat reaches you by infrared radiation. The other two methods rely on matter. Conduction occurs by particle interactions and vibrations transmitting energy through a solid (and to some extent through liquids and gases when there’s contact). Convection requires a moving fluid, where warmer, less dense regions rise and cooler, denser regions sink, carrying heat with the bulk motion. In a vacuum, where there’s no medium at all, conduction and convection can’t happen, leaving radiation as the only heat-transfer mechanism. So the true statement is that radiation does not require a medium.

Heat can move in three ways, and the one that doesn’t need any material to travel through is radiation. Radiation transfers energy through electromagnetic waves, so it can heat objects even across empty space. This is why the Sun can warm the Earth through the vacuum of space and why you feel warmth from a hot stove without touching it—the heat reaches you by infrared radiation.

The other two methods rely on matter. Conduction occurs by particle interactions and vibrations transmitting energy through a solid (and to some extent through liquids and gases when there’s contact). Convection requires a moving fluid, where warmer, less dense regions rise and cooler, denser regions sink, carrying heat with the bulk motion. In a vacuum, where there’s no medium at all, conduction and convection can’t happen, leaving radiation as the only heat-transfer mechanism.

So the true statement is that radiation does not require a medium.