What is the skin effect?
The skin effect is a usually undesirable effect which occurs when using AC signals. It causes the outer surface - the "skin" of the wire - to be used more than the inner surface for carrying current - engineers say the surface has a higher "current density", or amperes per meter squared. This causes an increase in the effective resistance of the wire.

Because the outer surface must carry more current the wire is more expensive, because you can't get rid of the inner surface easily. In electrical power distribution, the skin effect is very important, because it decides the type and thickness of the wire you use.

Skin depth reduces at higher frequencies. Carrying a 50 Hz signal takes less wire than a 1 kHz signal, for example. Skin depth also varies with the type of wire.

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