Thermal radiation
Heat that travels as infrared waves. It needs no material to travel through. Hot, dark, matt surfaces emit and absorb the most.
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Analogy
Feeling the warmth of a campfire on your face from across the clearing.
In practice
The Sun's heat reaches Earth across empty space by radiation. Shiny white surfaces reflect it.
Practice
Flashcards
- Which type of heat transfer needs no particles?Radiation.
Interview questions
- Describe how heat travels from a radiator to warm the whole room.
- Air touching the radiator is warmed by conduction
- Warm air expands, is less dense and rises
- Cool air sinks to replace it, forming a convection current
- Some heat also travels as infrared radiation
Questions people ask
Why can heat reach us from the Sun through space?
Space is almost empty, so conduction and convection cannot carry the energy there. Radiation does not need particles. The Sun gives out infrared waves, light and other electromagnetic waves, which cross space in about eight minutes and warm the surface of the Earth.
Why are cars painted white in hot countries?
Light, shiny surfaces reflect radiation instead of absorbing it, so the car stays cooler. A dark matt car absorbs more infrared and heats up quicker. For the same reason, a black kettle cools down faster than a shiny one because dark surfaces also emit heat better.