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 piepsilon_0) (qQ)/(4r^2)`
B. `1/(4 piepsilon_0) (9qQ)/(100r^2)`
C. `1/(4 piepsilon_0) (4qQ)/(25r^2)`
D. 0

Answer

D

Explanation

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