Infrared radiation and black bodies: Waves: Physics: GCSE (9:1)

Infrared radiation

Radiation that all bodies (objects) emit and absorb, no matter what temperature they are

Good absorbers and emitters of infrared radiation

Black and dull surfaces are the best absorbers and emitters, as they absorb all visible light wavelengths

Poor absorbers and emitters of infrared radiation

White and shiny silvery surfaces are the worst absorbers and emitters, as they reflect all visible light wavelengths

Effect of temperature on infrared radiation emissions

The hotter a body, the more infrared radiation it radiates in a given time and the greater proportion is emitted as visible light

Black body

A theoretical object that absorbs all of the radiation incident on it

Properties of a black body

It would absorb all the radiation that falls on it, would not reflect or transmit any radiation and would be the best possible emitter of radiation

Why stars are considered to be black bodies

They emit and absorb most wavelengths in the electromagnetic spectrum

Other examples of black bodies

Planets, black holes

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Rate of absorption and emission of infrared radiation

Determines whether the temperature of a body is increasing, decreasing or constant

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When an object's temperature is increasing

The rate of absorption of infrared is greater than the rate of emission

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When an object's temperature is decreasing

The rate of absorption of infrared is less than the rate of emission

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When an object's temperature is constant

The rate of absorption of infrared is equal to the rate of emission

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Factors affecting the Earth's temperature

The rates of absorption and emission of radiation, reflection of radiation into space, concentration of greenhouse gases in the atmosphere

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The greenhouse effect

Caused by naturally occurring greenhouse gases and stabilises the surface temperature of Earth