question_answer

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: [JEE Main Online Paper (Held On 09-Jan-2019 Morning]

A) \[R\sqrt{2}\]

B) R

C) \[\frac{R}{\sqrt{5}}\]

D) \[\frac{R}{\sqrt{2}}\]

Correct Answer: D

Solution :

\[E\,\,\,\,=\,\,\,\,\frac{kQx}{{{({{R}^{2}}+{{x}^{2}})}^{3/2}}}\] For \[{{E}_{\max }}\] \[\frac{dE}{dx}\,\,=\,\,0\] On solving we get \[x\,\,=\,\,\frac{R}{\sqrt{2}}\] So, option is correct.