Does electric current flow only on the surface of the copper conductor?

Answer 1

The AC current tend to flow on the surface of the conductor. The higher the frequency, the thinner the skin.

This is known as the skin effect. So DC current flow throught the entire conductor but when the signal varies (AC) there is the formation of eddy current in the conductor itself and that pushes the electrons at the surface of the conductor.

You can get more information on the skin effect and skin depth on wikipedia :

http://en.wikipedia.org/wiki/Skin_effect

http://en.wikipedia.org/wiki/Skin_depth

Answer 2

Electric current can flow through the entire volume of a copper conductor, not just on the surface. This is due to the free electrons within the conductor that can move throughout the material and carry the current. The skin effect, which causes higher frequencies to flow more on the surface, is typically only significant at very high frequencies.