Consider a system of three charges $\frac{\mathrm{q}}{3}, \frac{\mathrm{q}}{3}$ and $-\frac{2 \mathrm{q}}{3}$ placed at points $\mathrm{A}, \mathrm{B}$ and C , respectively, as shown in the figure. Take O to be the centre of the circle of radius R and angle $\mathrm{CAB}=60^{\circ}$