Question

Four charges +q, – q, + q and – q are to be arranged respectively at the four corners of a square ABCD of side ‘a’.

(i) Find the work required to put together this arrangement. 

(ii) A charge q0 is brought to the centre of the square, the four charges being held fixed. How much extra work is needed to do this?

Answer 1

(i) Work done in bringing charge +q at point A

W_A = 0

Work done in bringing charge –q to the point B

Work done in bring the charge +q to the point C

W_C = W_AC + W_BC

Work done in bringing a charge – q to the point D

W_D = W_AD + W_BD + W_CD

Total work done W = W_A + W_B + W_C + W_D