Brainlag PlusEvery object emits and absorbs infrared, perfect black bodies, how temperature changes the radiation, and the balance that sets the Earth's temperature.
Everything glows a little
All objects emit and absorb infrared radiation, whatever their temperature: a block of ice does too.
A perfect black body absorbs all the radiation that falls on it. It reflects and transmits none. A good absorber is also a good emitter, so a perfect black body is also the best possible emitter.
You can compare real surfaces with a Leslie cube: a metal cube of hot water whose four sides are matt black, shiny black, matt white and shiny silver. An infrared detector held the same distance from each side shows matt black emits most and shiny silver least. The water temperature and the distance are control variables.
The rest of this lesson and its 10 practice questions are in Plus.
Screen 1 of 4, free to read.
- 10 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards