Four electric charges +q, +q, -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 charges +q and +q, is +9 1 2q 4 L 1 2q 4E L 1 2q 4E L (a) (b) (c) (d) zero +q (1 + 5) (1 + 5) (1 - -/-) 9