# Three charged particles in equilibrium [closed]

Suppose two particles each having charge $q$, are placed at a separation. What charge $Q$ should be placed at the midpoint between them, so that all the three may remain in equilibrium

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This possibly looks like a homework question – Ϛѓăʑɏ βµԂԃϔ Aug 26 '12 at 16:42
Not exactly homework, this is problem from the book I tried to solve but got stuck, please help. – pritam Aug 26 '12 at 16:47
"Homework" does not mean that the problem was necessarily assigned. Merely that the problem is of a pedagogical nature, and as per our FAQ, we don't entertain such questions in their raw form (as here). If you could edit the question to concentrate on what conceptual difficulty is preventing you from proceeding, I (or another mod) can re-open this question. Just flag for attention when you are done. – dmckee Aug 26 '12 at 19:15

## closed as too localized by dmckee♦Aug 26 '12 at 19:15

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## 1 Answer

This is a standard question asked in pretty much any first course on electrostatics. As such, rather than give the full answer, I'll point out that equilibrium is achieved when there is no net force on any particle. When it comes to forces on static charges, Coulomb's Law is the only equation to choose from. Try balancing the forces using this.

As an added bonus, see if you can prove the instability of the system. Which way does a perturbed force push/pull a particle that has been slightly displaced in this system?

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