Question

For a uniformly charged ring of radius R, the electric field on its axis has the largest magnitude at a distance h from its centre. Then value of h is :

(1) $R\over\sqrt5$

(2) $R$

(3) $R\over\sqrt2$

(4) $R\sqrt2$

Answer 1

Ans: (3) $R\over\sqrt2$

Sol: Electric field on axis of ring

$E={kQh\over(h^2+R^2)^{3/2}}$

for maximum electric field

${dE\over dh}=0$

$\implies h={R\over\sqrt2}$

Answer 2

Ans:(3) $R\over\sqrt2$