Radiation

Definition

Radiation is the transfer of energy through electromagnetic waves without requiring a medium. It can occur in a vacuum and is responsible for the heat we receive from the sun.

5 Must Know Facts For Your Next Test

1. Unlike conduction and convection, radiation does not require a medium to transfer heat.
2. The power radiated by an object is proportional to the fourth power of its absolute temperature, as described by the Stefan-Boltzmann law.
3. All objects emit some level of radiation, but hotter objects emit more and at shorter wavelengths.
4. The Earth receives solar energy primarily through radiation from the Sun.
5. Radiation can be absorbed, reflected, or transmitted when it interacts with matter.

Review Questions

• How does radiation differ from conduction and convection in terms of heat transfer?
• What law describes the relationship between an object's temperature and the power it radiates?
• Can radiation occur in a vacuum? Explain your answer.

Related terms

Conduction:

The transfer of heat through direct contact between molecules within a material.

Convection:

The transfer of heat by the movement of fluids (liquids or gases) due to differences in temperature and density.

Stefan-Boltzmann Law: $$P = \sigma A T^4$$ where $P$ is the power radiated, $\sigma$ is the Stefan-Boltzmann constant, $A$ is the surface area, and $T$ is the absolute temperature.