In DC circuits the charge carriers move uniformly through the entire cross sectional area of the wire. In AC circuits the current is constrained to travel in a thin "skin" just below the surface of the wire, effectively reducing the cross-sectional area of the wire. The effect becomes more pronounced the higher the frequency of the AC circuit. Can anyone please give me a physical explanation of why the charge carriers are confined to the "skin" in an AC circuit. Or could you please direct me to a source where this is worked out explicitly? Thank you!