Three charges -q, +q and -q are placed along a st. line at equal distance , say a. Calculated the potential energy of this system of charges (i) when +q charge is in the middle and (ii) when this charge is at one end.

Answer

(i). `-(3q^(2))/(8piepsi_(0)r), (ii) `-(q^(2))/(8piepsi_(0)r)`