# a point chargeQis located on the axis of a disc of radiusRat a distance b from the plane of the disc .Show that if one-fourth of the electric flux from the charge passes through the disc ,then R=root3b

Arun Kumar IIT Delhi
8 years ago
`Assuming a sphere with radius b and center a charge q.$\small \phi_{\theta}=q(1-cos(\theta))/2\epsilon=q/4\epsilon \\=>cos(\theta)=1/2 \\=>b/(b^2+R^2)=1/2 \\=>4b^2=b^2+R^2 \\=>3b^2=R^2 \\=>R=\sqrt3b$Thanks & RegardsArun KumarIIT DelhiAskiitians Faculty`