Class 12 Physics, CBSE and UP Board, Electrostatic Potential and Capacitance,Chapter-2 Exercise 2.4, NCERT Solutions for Class 12 Physics
A spherical conductor of radius 12 cm has a charge of 1.6 × 10^⁻7 C distributed uniformly on its surface. What is the electric field (a) inside the sphere (b) just outside the sphere (c) at a point 18 cm from the centre of the sphere?
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Ans (a).
Radius of the spherical conductor, r = 12 cm = 0.12 m
Charge is uniformly distributed over the conductor, q = 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.
Ans (b).
Electric field E just outside the conductor is given by the relation,
E=1/4πε0 x q/r²
Where, ε0 = Permittivity of free space and = 9 x 109 Nm2C⁻²
Therefore, E = (9x 109 x 1.6 x 10-7)/(o.12)²
=10⁵ NC⁻¹
Therefore, the electric field just outside the sphere is 105 NC-1.
Ans (c).
Electric field at a point 18 m from the centre of the sphere = Ei
Distance of the point from the centre, d = 18 cm = 0.18 m
1 q 9 x 109 x 1.6 x 10-7
E=1/4πε0 x q/d²
= (9x 109 x 1.6 x 10-7)/(1.8 x 10⁻² )²
= 4.4 x 10⁴ NC-1
Therefore ,the electric field at a point 18cm from the centre of the sphere is 4.4 x 10⁴ NC-1