(b) Potential at the centre $O,\ V = 4 \times \frac{1}{4\pi\varepsilon_{0}}.\frac{Q}{a/\sqrt{2}}$
[image:1_image309.wmf]Where $Q = \frac{10}{3} \times 10^{- 9}C$ and $a = 8cm = 8 \times 10^{- 2}m$
So $V = 4 \times 9 \times 10^{9} \times \frac{\frac{10}{3} \times 10^{- 9}}{\frac{8 \times 10^{- 2}}{\sqrt{2}}} = 1500\sqrt{2}\ volt$