Abstract: When an uncharged conductor is moved to the electric field produced by a point charge, there will be induced charge distribuion on the surface of the conductor. It is proved that for conductor with arbitrary shape, the interaction energy between the point charge and the conductor is half of the coulomb interaction energy between the point charge and image charges. Furthermore a very simple understanding to this result is provided.

Key words: conductor, point charge, induced charge, interaction energy, electric image method