The skin effect causes AC current density J in a conductor decreases exponentially from its value at the surface J_S according to the depth d from the surface.

The skin effect causes AC current density J in a conductor decreases exponentially from its value at the surface J_S according to the depth d from the surface. The depth decreases as the square root of frequency. This means that the effective power a wire can carry decreases with increasing AC frequency. https://en.wikipedia.org/wiki/Skin_effect#Formula https://en.wikipedia.org/wiki/Skin_effect#Formula