Point charges `– q, 2q, – 3q, q, – q, 2q, – 3q, q, – q, 2q, – 3q`, and q have been placed at marks `1, 2, 3, 4, 5 .....12` respectively on the circular dial of a clock. Find the electric field intensity at the centre of the dial if distance of each charge from the centre is r.

Answer

zero.