Four particles carrying charges + 2q, − 2q, + 4q and − 4q (with q = 1.0 nC) are kept at
the vertices of a square of side 6.0 cm. Determine the net electric field due to these
charged particles at the centre of the square. What is the electrostatic force on a
particle carrying positive charge of 1.0 nC placed at the centre of the square
