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.