Three positive charges of equal magnitude q are placed at the vertices of an equilateral triangle of side l. How can……

Q. Three positive charges of equal magnitude q are placed at the vertices of an equilateral triangle of side l. How can the system of charges be placed in equilibrium?

(a)by placing a charge Q = −q/√3 at the centroid of the triangle

(b)by placing a charge Q = −3q/√3 at the centroid of the triangle

(c)by placing a charge Q =  q at a distance l from all the three charges

(d)by placing a charge Q = −q above the plane of the triangle at a distance l from all the three charges

Ans: (a)