There is a cubical cavity inside a conducting sphere of radius R. A positive point charge Q is placed at the centre of the cube and another positive charge q is placed at a distance `1(gtR)` from the centre of the sphere. The sphere is earthed

Net charge on the outer surface of conducting sphere is

Options

A. `+Q`
B. `Q-qR//1`
C. `-qR//I`
D. none

Answer

C

Explanation

Potential of the sphere is zero as it is earthed so potehtial at the centre, v=0
`Rightarrowv=(Kq)/l+(QE)/R=0`
`Q^(1)`=charge induced on the surface of the sphere
`Rightarrow Q^(1)=(-qR)/l`