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) $R\sqrt2$
(1) $R\over\sqrt5$
(2) $R$
(3) $R\over\sqrt2$
(4) $R\sqrt2$