Properties of conductors

1. There is no electric field inside a conductor.
   Otherwise, the charges in the conductor would move.

2. Charges exist only on the surface of a conductor.
   Otherwise, there would be electric fields inside.

3. All points of a conductor are at the same potential.
   Since DV=-EDx, and E=0, the potential must be constant.

Conductors are materials such as copper, aluminium, silver... They usually are metals. The fact that electric fields do not penetrate into conductors explains why light, which is an electromagnetic wave, also does not penetrate into a metal. A radio wave, which is just a long wavelength light signal, does not propagate underneath a bridge or into a tunnel because of the steel reinforcements in the concrete.

Examples     Gauss's law/conductors main page