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

TL;DR

This paper demonstrates that the electrostatic force between a point charge and a neutral metallic object can be repulsive in certain geometries, challenging the common assumption of always attractive forces.

Contribution

The authors provide the first example of a geometry where electrostatic force is repulsive, supported by analytical and exact calculations, with implications for related physical systems.

Findings

Repulsive electrostatic force observed in specific geometry

Analytical and exact calculations confirm the repulsion

Implications for Casimir and other physical systems

Abstract

We give an example of a geometry in which the electrostatic force between a point charge and a neutral metallic object is repulsive. The example consists of a point charge centered above a thin metallic hemisphere, positioned concave up. We show that this geometry has a repulsive regime using both a simple analytical argument and an exact calculation for an analogous two-dimensional geometry. Analogues of this geometry-induced repulsion can appear in many other contexts, including Casimir systems.