question_answer

Let a total charge 2Q be distributed in a sphere of radius R, with the charge density given by \[\rho (r)=kr,\]where r is the distance from the centre. Two charges A and B, of -Q each, are placed on diametrically opposite points, at equal distance, a, from the centre. If A and B do not experience any force, then: [JEE Main 12-4-2019 Afternoon]

A) \[a=\frac{3R}{{{2}^{{}^{1}/{}_{4}}}}\]

B) \[a=R/\sqrt{3}\]

C) \[a={{8}^{-1/4}}R\]

D) \[a={{2}^{-1/4}}R\]

Correct Answer: C

Solution :

[c]