A sperical shell of radius R with uniform charge q is expanded to a radius 2R. Find the work perfomed by the electric forces and external agent against electric forces in this process.

Explanation

`W_("ext") = U_(f) - U_(i) = (q^(2))/(16pi epsilon_(0)R) - (q^(2))/(8pi epsilon_(0)R) = -(q^(2))/(16pi epsilon_(0)R)`
`W_("ext") = U_(i) - U_(f) = (q^(2))/(8pi epsilon_(0)R) - (q^(2))/(16pi epsilon_(0)R) = (q^(2))/(16pi epsilon_(0)R)`