Planck's law of black body radiation

In physics, the spectral intensity of electromagnetic radiation from a black body at temperature T is given by the Planck's law of black body radiation:

Related Topics:
Physics - Electromagnetic radiation - Black body

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:I( u) =rac{2h u^{3}}{c^2}rac{1}{expleft(rac{h u}{kT} ight)-1}

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where:

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:I(ν) is the amount of energy per unit time per unit surface area per unit solid angle per unit frequency. Units are e.g. ;

Related Topics:
Energy - Time - Surface area - Solid angle - Frequency

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:ν is the frequency

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:T is the temperature of the black body

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:h is Planck's constant,:

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:c is the speed of light

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:k is Boltzmann's constant.

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The law is sometimes written in terms of the spectral energy density

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:u( u)=rac{8pi h u^3 }{c^3}~rac{1}{e^{h u/kT}-1}

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which has units of energy per unit volume per unit frequency.

Related Topics:
Energy - Volume - Frequency

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Max Planck originally produced this law in 1900 (published in 1901) in an attempt to improve upon an expression proposed by Wilhelm Wien which fit the experimental data at short wavelengths but deviated from it at long wavelengths. He found that the above function fit the data for all wavelengths remarkably well.

Related Topics:
Max Planck - 1900 - 1901 - Wilhelm Wien

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In constructing a derivation of this law, he considered the possible ways of distributing electromagnetic energy over the different modes of charged oscillators in matter. Planck's law emerges

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if it is assumed that these oscillators have energy proportional to frequency

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E=h u,.

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