Question

Two thin concentric and coplanar spherical shells, of radii a and b (b > a) carry charges, q and Q, respectively. Find the magnitude of the electric field, at a point distant r, from their common centre for.

(i) 0 < x < a

(ii) a < x < b

(iii) b < x < ∝

Answer 1

(i)  For 0 < x < a

Point lies inside both the spherical shells. Hence,

E(x) = 0

(ii) For a < x < b

Point is outside the spherical shell of radius 'a' but inside the spherical shell of radius 'b'.

(iii) For b < x < ∝

Point is outside of both the spherical shells. Total effective charge at the centre equals (Q + q).