What is radiation?

• A. The transfer of energy by electromagnetic waves
• B. The transfer of energy by convection
• C. The transfer of energy by conduction
• D. The transfer of energy by chemical reactions

Answer: (C)

Radiation is the transfer of energy by electromagnetic waves. It does not require matter to move the energy, so it can travel through empty space. This is why you can feel warmth from the Sun or a fire without touching them—the energy is traveling through the air or even through space as electromagnetic waves, often in the infrared part of the spectrum when we talk about heat.

In infrared thermography, the object emits infrared radiation based on its temperature and surface properties, and the camera senses that radiation to create an image of temperature differences. This is a practical example of radiation in action.

Conduction, by contrast, transfers energy through direct contact, molecule to molecule, typically within solids or between touching materials. Convection moves energy via the bulk motion of fluids, carrying heat with rising warm air or circulating water. Chemical reactions can release or absorb heat, but that’s energy change from chemical processes rather than a mode of heat transfer by waves or movement of matter.

So radiation stands out because it is energy moving through space itself via electromagnetic waves, not requiring a medium or contact to transmit heat.