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We give an example of a geometry in which the electrostatic force between apoint charge and a neutral metallic object is repulsive. The example consistsof a point charge centered above a thin metallic hemisphere, positioned concaveup. We show that this geometry has a repulsive regime using both a simpleanalytical argument and an exact calculation for an analogous two-dimensionalgeometry. Analogues of this geometry-induced repulsion can appear in many othercontexts, including Casimir systems.

Is the electrostatic force between a point charge and a neutral metallic object always attractive?