A remaining question is how large the induced charges are. The movement of charges is caused by the force exerted on them by the electric field of the external charged object, by Coulomb's law. As the charges in the metal object continue to separate, the resulting positive and negative regions create their own electric field, which opposes the field of the external charge. This process continues until very quickly (within a fraction of a second) an equilibrium is reached in which the induced charges are exactly the right size and shape to cancel the external electric field throughout the interior of the metal object. Then the remaining mobile charges (electrons) in the interior of the metal no longer feel a force and the net motion of the charges stops.
