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The conditions of equilibrium are obtained for a charged test particle in the field of a spherical charged mass. Einstein-Maxwell theory is used. The classical condition q1q2=Gm1m2 is neither necessary nor sufficient, whereas q1=+or-G12/m1, q2=+or-G12/m2 is sufficient but not necessary. There are also separation-dependent equilibrium positions, and some of these allow the charges to have opposite signs. Stability to radial displacements is investigated.
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W. B. Bonnor (1993) studied this question.
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