Question

how is the resistence of a cooper conductive material at 20°c.
if the current is dc, then is ac 60 hz then 5khz

Answer 1

There's and approximation for various frequencies, its known as the skin effect. It's a function of the square root of frequency and conductivity(at a specific temperature), seeing your asking the question you should have access to the equation. The skin depth actually becomes the new area, and with circular wire it's annulus area times the resistivity.