At each of the four vertices of a square of side 10 cm there is a +20 esu of charge. Find the Intensity of electric fleld at the point of Intersection of the two dlagonals.

Explanation

The point of intersection O of the diagonals is equidistant from four equal charges [Fig. 2.25]. So the electric field at O due to each charge is the same in magnitude (= E, say).

Now, the fields E along `vae(OC)` and E along `vec(OA)` cancel each other. Similarly, E along `vec(OD)` and E along `vec(OB)` also cancel.
Therefore, intensity of the electric field at the point of intersection of the two diagonals of the square is zero.