We know that that when a metal is exposed to light then metal gets heated after some time. The reason behind this as follows.
In metals there are large number of free electrons, these electrons interact with the optical electric field. Due to this field motion of electrons are damped by collision with the vibrating lattice of the material and hence a part of energy dissipated in the form of heat.
Skin depth and skin layer:
When light passes through a metal its intensity decreases with respect to the distance through which it propagates through the metal. Therefore the energy of the light decreases due to the absorption of light by free electrons.
Thus the skin depth is the maximum distance upto which as electro-magnetic wave (light) can travel thereby producing conduction current due to the interaction of light with free electrons. The conduction current which passes upto a layer is called skin layer.
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