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Radiation
Beginner
Heat transfer by EM waves, needing no medium.
All bodies emit electromagnetic radiation depending on temperature, needing no medium. Dark, rough surfaces absorb and emit better than shiny ones.
Sunlight warms Earth through vacuum.
A hot object radiates even when surrounded by hotter air.
In more detail
Radiation transfers heat by electromagnetic waves, requiring no medium. All objects emit thermal radiation, and the rate increases steeply with temperature.
Real-world uses
- The Sun warms Earth through radiation across space.
- Infrared heaters warm objects directly without heating the air.
- The Sun warms the Earth across empty space by radiation, which needs no medium to transfer its energy.
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Frequently asked questions
Can heat travel through a vacuum?
Yes, only by radiation, since conduction and convection need matter.
Why do dark surfaces get hotter in sun?
Dark surfaces absorb more radiation and emit less efficiently than light ones.
Does a dark surface radiate more heat?
A good absorber is also a good emitter, so dark surfaces radiate strongly at the same temperature.
Related topics in Heat & Thermodynamics
Conduction · Thermal resistance · Convection · Stefan–Boltzmann law · Newton's law of cooling · Wien's displacement law