There are two point charges of +1C each separated by 10m in vacuum. Calculate the change in potential energy of the system if they are brought to a separation of 5m.
9×108J
Change in potential energy will simply be final P.E minus initial P.E.
ΔPE=kQqrf−kQqri=kQq(1rf−1ri)=9×109(15−110)=9×108J