6.12 - Absorbing & Emitting Radiation

Infrared emission and absorption

• Every object constantly emits and absorbs infrared radiation from its surface.
• The hotter an object is, the more infrared radiation it emits in a given time.

Emission vs absorption sets the temperature

• Emits more than it absorbs - The object cools down (e.g. a mug of hot tea cooling).
• Emits less than it absorbs - The object warms up (e.g. a glass of iced water on a warm day).
• Emits at the same rate as it absorbs - The object stays at the same temperature.

How surfaces affect emission and absorption

• A matt black surface is the best absorber and the best emitter of radiation.
• A light, shiny surface is a poor absorber and a poor emitter, but the best reflector of radiation.