At what distance should two charges of 5 nC and 6 nC be located so that they repel with a force of 0.12 mN.

We calculate the distance between charges using Coulomb’s law:

F = k * | q1 | * | q2 | / r², where F is the force with which the charges are repelled (F = 0.12 mN = 0.12 * 10 ^ -3 N), k is the proportionality coefficient (for air, vacuum k = 9 * 109 N * m² / Kl² ), q1 is the first charge (q1 = 5 nC = 5 * 10 ^ -9 C), q2 is the second charge (q2 = 6 nC = 6 * 10 ^ -9 C), r is the distance at which the charges must be placed.

r = √ (k * q1 * q2 / F).

Payment:

r = √ (9 * 10 ^ 9 * 5 * 10 ^ -9 * 6 * 10 ^ -9 / 0.12 * 10 ^ -3) ≈ 0.047 m = 47 mm.