# Temperature and EM waves.

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• #1
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What exactly is tempertaure?
As far as I know it represents the average vibration of atoms.
How it relates to EM wave? because I have read in many Physics texts saying that 'the temperature of this wave is X Kelvin'. How do they find the temperature of individual EM wave?

Correct me if I am wrong for following:
Suppose an aluminium rod and wood are at room temperature;In case of Aluminium rod the atoms as well as free electrons would contribute to its temperature. For wood I think only the atoms will contribute.

• #2
f95toli
Gold Member
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How it relates to EM wave? because I have read in many Physics texts saying that 'the temperature of this wave is X Kelvin'. How do they find the temperature of individual EM wave?

It is not really the temperature of the EM wave. "Temperature" can here mean one of two things: either the temperatures of the object that EMITTED the wave (which can be calculated using Wien's displacement law, or more generally Planck's law) or it simply means that they multiplied the frequency by Planc's constant (=the energy if the photons) and then divided by Boltzmann's constant. $T=\hbar \omega/k_B$

The latter is actually quite common and is done for convenience when dealing with some systems, note that you can obviously also invert this relationship and measure "temperature" in units of Hz (something I use quite frequently) or measure potential energy in Kelvins.

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