A spherical conductor with a spherical cavity carries an exc

A spherical conductor with a spherical cavity carries an excess charge of +7Nc. Inside the cavity, insulated from the conductor is a point charge of -5Nc. a. Use Gauss\' Law to determine how much charge is on the surface of the spherical cavity. b. If the total excess charge +7nC, what is the charge on the surface of the spherical conductor?

Solution

(A) Field inside conductor is alway zero.

and from Gauss\' LAw,

total flux from closed surface = E. A = Qinside / e0

if E = 0 then Qinside =0

so for any point inside conductor, Qin must be zero.

and charge on cnductors always lies on surface.

Qin = - 5 nC + Qinner = 0

Qinn = 5 nC .....Ans (Surface on inner surface Or cavity surface)

(b)
total charge on onductor = Qinn + Qout = +7 nC

5 + Qout = 7

Qout = 2 nC