University Physics II · Electric field and Gauss law
A third charge balances a symmetric pair
Problem
Two fixed charges $+Q$ are at $x=-a$ and $x=+a$, with $Q,a>0$. A third charge $q$ is placed at the origin. Find $q$ so that all three charges are in equilibrium, and verify the condition for each charge.
Hint
Use reflection symmetry to check the force on the central charge.
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