Q 2.4) A spherical conductor of radius 12 cm has a charge of 1.6 x 10-7C distributed uniformly on its surface. What is the electric field

(1) inside the sphere.

(2) just outside the sphere.

(3) at a point 18 cm from the centre of sphere.

 
(a) Radius of the spherical conductor, r = 12 cm = 0.12 m
Charge is uniformly distributed over the conductor, q = 1.6 x 10-7 C
Electric field inside a spherical conductor is zero. This is because if there is field inside the conductor, then charges will move to neutralize it.
(b) Electric field E just outside the conductor is given by the relation,
E=14πε0qr2
Where, E = Permittivity of free space and14πε0=9×109Nm2C2
Therefore, 
E=9×109×1.6×107(0.12)2=105NC1
Therefore, the electric field just outside the sphere is 105 NC-1 NC
(c)Electric field at a point 18 m from the centre of the sphere E
The distance of the point from the centre, d = 18 cm 0.18 m
E1=14πε0qd2=9×109×1.6×107(1.8×102)2=4.4×104NC1
Therefore, the electric field at a point 18 cm from the center of the sphere is 4.4 x 104 NC-1