Thermal Radiation

Someone is warming their hands over a bonfire. They don’t have to touch the fire to feel its warmth. Then how does the heat travel from the fire to their hands?

This happens through thermal radiation, the transfer of thermal energy through invisible waves.

These waves are called electromagnetic waves, which do not need a medium like air or water to travel. They can even move through empty space.

Thermal energy is the energy of moving particles in a substance. When this energy flows from a warmer object to a cooler one—like from the warm air near a heater to the cooler parts of a room—it is called heat.

Here, the bonfire emits heat in the form of electromagnetic waves. These waves reach the person’s hands, making them feel warm.

Unlike conduction, which requires direct contact, or convection, which requires a medium to travel, radiation does not need any matter to transfer heat.

The Sun’s heat reaches us through radiation. Even though space is a vacuum with no air or matter, the Sun’s energy still travels through it and warms Earth.