Three charges +4q, Q and q are placed in a straight line of length l at coordinates (0, 0), (l/2, 0) and (l, 0) respectively. What should be Q in order to make the net force on q to be zero?

Five identical capacitors each of value 2 F are connected between the pair of nodes (a,c), (c,d), (a,d)(b,d) and (c,b). If all the capacitors are initially uncharged, the equivalent capacitance between the nodes a and b will be

The electric field at the origin is along the positive X-axis. A small circle is drawn with the

centre at the origin cutting the axes at points A, B, C and D having coordinates (a, 0) (0, a),

(–a, 0), 0, –a) respectively. Out of the points on the periphery of the circle, the potential is

minimum at