The proposed problem is to calculate the charge to be placed in the center of a ring, in which we distribute n charges equal to q, so that the constraint force become null. The solution for this problem is to place a charge Q of opposite sign in the center of the ring, so the sum of electric forces in each charge in the ring, due to the central charge and the other charges, become null. We search for a function Q(nq) that gives the value of Q in terms of nq. The result is that Q(nq) is proportional to n ln(n)q for n <img border=0 width=32 height=32 src="http://img/fbpe/rbef/v23n2/smama.gif">2.
