The simplest example of method of image charges is that of a point charge, with charge q, located at ( 0 , 0 , a ) above an infinite grounded (i.e.: V = 0 ) conducting plate in the xy -plane. To simplify this problem, we may replace the plate of equipotential with a charge − q, located at ( 0 , 0 , − − a ) . This arrangement will produce the same electric field at any point for which z > 0 (i.e., above the conducting plate), and satisfies the boundary condition that the potential along the plate must be zero. This situation is equivalent to the original setup, and so the force on the real charge can now be calculated with Coulomb's law between two point charges.