Emitting Radiation
Physics: Cambridge International GCSE Supplement, topic 2.3.6
Emitting Radiation
The amount of radiation emitted by a body (object) depends on its surface area and surface temperature.
High surface temperature
- Bodies with a higher surface temperature will emit radiation faster.
High surface area
- Bodies with a large surface area will emit radiation faster.
Constant temperature
- Bodies are at a constant temperature when the rate of energy absorbed is equal to the rate of energy emitted by the body.
- If a body absorbs more energy than it emits, its temperature increases.
- If a body emits more energy than it absorbs, its temperature decreases.
The Earth’s temperature
- The temperature of the Earth depends on the balance between:
- Incoming radiation from the Sun (mainly visible light and short-wave infrared).
- Outgoing radiation emitted by the Earth’s surface (mainly longer-wave infrared).
- If the Earth absorbs more energy from the Sun than it emits, its average temperature increases.
- If the Earth emits more energy than it absorbs, its average temperature decreases.
- If the rates are equal, the temperature remains constant.
Test yourself on Emitting Radiation
Which of the following is true of emitters?
How does surface temperature affect the rate of emission of radiation?
If one thermometer has a black bulb and the other has a shiny foil bulb, which will have the higher temperature if both are heated?