Four electric charge +q, +1, - q and -q are placed at the corners of a square of side 2L. (see figure). The electric potential at point A, midway between the two charge +q and +q, is : <br>

Question

( A ) $\frac{1}{4 \pi \epsilon _0} \frac{2q}{L} (1 - \frac{1}{\sqrt {5}})$
( B ) $\frac{1}{4 \pi \epsilon _0} \frac{2q}{L} (1 + \frac{1}{\sqrt {5}})$
( C ) zero
( D ) $\frac{1}{4 \pi \epsilon _0} \frac{2q}{L} (1 + \sqrt {5})$