A spherical shell of radius `R_(1)` with uniform charge q is expanded to a radius `R_(2)`. Find the work performed by the electric forces in this process.

Explanation

As the field is conservative total work done by field force,
`A_(fd) = U_(i) - U_(f) = (1)/(2) q (varphi_(1) - varphi_(2))`
`= (1)/(2) (q^(2))/(4pi epsilon_(0)) [(1)/(R_(1)) - (1)/(R_(2))] = (q^(2))/(8pi epsilon_(0)) [(1)/(R_(1)) - (1)/(R_(2))]`