This is an abstract of my book " Potential energy is always defined relative to some reference point where U=0. Therefore U represents the work that would be on the test charge q0 by the field of q if q0 moved from an initial distance r to infinity. If q and q0 have the same sign, the interaction is repulsive, this work is positive, and U is positive at any finite separation. If the charges have opposite signs, the interaction is attractive, the work done is negative and U is negative" ... All right, let's take this into small parts. I agree that U is zero at infiinity following the formula U = kq1q2/r .. Now, we know Work done is the negative of delta. U. Taking the second sentence, shouldn't work be done by a force and the electric field does no work. Now, with the first condition when both charges are positive. which work is positive. Which work is actually referred in this text. I assume it is the work done due to the field of let us say q on q0. If so, why is U positive then. When they have opposite charges, I don't get why is the work negative. I need clarification for this confusing text. I am sorry it is a bit long but try being patient with me and thanks a lot to whoever shares his ideas.