Charge of $+q, +2q, + q$ and $−q$ are placed at the corners of a square ABCD, calculate the electric field at the intersection of the diagonals of the square when $q = 5/3 × 10^{-9} C$ and each side square of is 10 cm.

$0.9×10^4Vm^{-1}$

Electric field due to charge at corner A and D will cancel each other out. Electric field due to charge 2q and -q will add up.

Length of diagonal is $10\sqrt{2}$ cm. half of diagonal =$5\sqrt{2}$ cm

E = $\frac{1}{4\pi\epsilon_0}\frac{3q}{(5\sqrt{2} cm)^2}$ = 9 $\times 10^3$