Asked by  | 21st Feb, 2010, 03:37: PM

Expert Answer:

Dear student,

It can be proved by contradiction. Suppose the equilibrium is stable, then if the test charge if displaced slightly in any direction will experience a restoring force towards the null point. That is all the filed lines near the null point should be directed towards the null point inwards. Thus, there is net inward electric flux of electric field through a closed surface around the null point. But, by Gauss's law, the flux of electric field through a surface not enclosing any charge must be zero. Hence, the equilibrium cannot be stable.

Hope this helps.

Answered by  | 22nd Feb, 2010, 03:32: PM

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