6.4.1 Black Body Radiation

General Properties of Radiation

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All objects, regardless of their temperature, emit and absorb infrared radiation.

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Hotter Objects:

Emit more radiation per second, meaning they release energy more rapidly.
Emit radiation with shorter wavelengths, which have more energy (e.g., X-rays).

Black Body

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A black body is an idealized object that absorbs all the radiation it receives. It does not transmit or reflect any radiation.

Because it absorbs all radiation, it also emits radiation across all wavelengths. This makes it a perfect emitter.

Radiation and Temperature Balance

A body at a constant temperature continues to emit and absorb radiation.
- At constant temperature, the rate of radiation absorption equals the rate of radiation emission, maintaining thermal equilibrium.
If a body's temperature increases, it means it is absorbing more energy than it is emitting.
If a body is cooling down, it is emitting more energy than it is absorbing, leading to a decrease in temperature.

Additional Context:

Space and Black Body Radiation:
- In space, black body radiation plays a critical role in understanding how stars, planets, and other celestial bodies emit energy. Stars, for example, can be approximated as black bodies, with their color indicating their temperature (hotter stars appear blue, cooler stars appear red).

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Real-World Example: The Earth absorbs radiation from the Sun and emits infrared radiation back into space. The balance between absorption and emission determines the Earth's temperature, which is crucial for understanding climate and energy.

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