Question

Four point charges `q_(A) = 2 mu C , q_(B) = -5 mu C, q_(C) = -2 mu C and q_(D) = -5 mu C` are located at the corners of a square ABCD of side 10 cm. What is the force on a charge of `1 mu C` placed at the center of the square ?

Answer 1

In Fig, length of diogonal of the square
`= AC = BD = sqrt(10^(2) + 10^(2)) = 10 sqrt(2) cm`.
`OA = OB = OC = OD = (10 sqrt(2))/(2) = (10)/(sqrt(2)) cm`.
Force of repulsion on `1 mu C` charge on O due to `2 mu C` charge, at A and C are equal and opposite . Therefore, they cancel.
Similarly, force of attraction on `1muC` charge at 0, due to `-5 mu C` charges at B and D are also equal and opposite , Therefore, these also cancel.
Hence the net force on the charge of `1 mu C` at 0 is Zero.