Consider an initially neutral hollow conducting spherical shell with inner radius r and outer radius 2r. A point charge +Q is now placed inside the shell at a distance r/2 from the centre. The shell is then grounded by connecting the outer surface to the earth. P is an external point at a distance 2r from the point charge +Q on the line passing through the centre and the point charge +Q as shown in the figure.

The magnitude of the force on a test charge +q placed at P will be

Options

A. `(1)/( 4 pi epsi_0) (qQ)/(4r^(2))`
B. `(1)/(4 pi epsi_(0)) (9qQ)/(100r^(2))`
C. `(1)/(4 pi epsi_0)(4 qQ)/(25 r^(2))`
D. 0

Answer

D

Explanation

Charge on outer most surface is zero
Hence force on q is also 0