Question

Find the force between two charges when they are brought in contact and separated by 4cm apart, charges are 2nC and -1nC, in μN.

(a) 1.44

(b) 2.44

(c) 1.404

(d) 2.404

I have been asked this question during an online interview.

My question is based upon Coulomb Law topic in division Electrostatic Fields of Electromagnetic Theory

Answer 1

Right answer is (c) 1.404

Easy explanation: Before the charges are brought into contact, F = 11.234 μN.

After charges are brought into contact and then separated, charge on each sphere is, (q1 + q2)/2 = 0.5nC

On calculating the force with q1 = q2 = 0.5nC, F = 1.404μN.