Figure shows a uniformly charged sphere of radius R and total charge Q. A point charge q is situated outside the sphere at a distance r from centre of sphere. Find out the following :
(i) Force acting on the point charge q due to the sphere.
(ii) Force acting on the sphere due to the point charge.

Explanation

(i) Electric field at the position of point charge
`vec(E) = (KQ)/(r^(2)) hat(r )`
so, `vec(F) = (KqQ)/(r^(2)) hat(r ) |vec(F)| = (KqQ)/(r^(2))`
(ii) Since we know that every action has equal and opposite reaction so
`vec(F)_("sphere") = -(KqQ)/(r^(2)) hat(r )`
`|vec(F)_("sphere")| = (KqQ)/(r^(2))`.