Question

Four point charges of 1μC, −2 μC, 1 μC and −2 μC are placed at the corners A, B, C and D respectively, of a square of side 30 cm. Find the net force acting on a charge of 4 μC placed at the centre of the square.

Answer 1

The forces of repulsion on charge 4 μC ue to charge 1μC at A and C are equal and opposite. Hence, they cancel each other.

Similarly, the forces of attraction on charge 4 μC due to charge −2 μC at B and D are equal and opposite. Hence, they also cancel each other. So, the net force acting on the charge at the centre is zero.