A) for all values of H
B) only if \[H>R/\sqrt{2}\]
C) Only if \[H<R/\sqrt{2}\]
D) \[H=R/\sqrt{2}\]
Correct Answer: B
Solution :
We know that due to charged ring the electric field is maximum at \[{{=}^{9}}{{C}_{5}}{{-}^{7}}{{C}_{5}}=104\]. The particle be in equilibrium, at H such that mg downwards is equal to qE upwards. If \[=\alpha +\beta \], the equilibrium is stable since on increasing H mg is same but E decreases hence mg > qE and hence mg brings down the charge the particle moves back to the equilibrium position. But when we decrease H, E decreases but mg same hence now mg brings down and the charge do not return to its original position hence behaviour becomes unstable.
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