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))hatr`
so, `" "vecF=("KqQ")/(r^(2))hatr" "|vec"F"|=("KqQ")/(r^(2))`
(ii) Since we know that every action has equal opposite reaction so
`vecF_("sphere")=-("KqQ")/(r^(2))hatr`
`|vec(F)_("sphere")|=("KqQ")/(r^(2))`