At what distance from each other the charges of 7 nC and 9 μC interact with a force of 3 mN?

1. Let’s translate all values from given to SI system:
q1 = 7 nC = 7 * 10 ^ -9 C
q2 = 9 μC = 9 * 10 ^ -6 CL
F = 3mH = 3 * 10 ^ -3H
2. The force of interaction between charges according to Coulomb’s law:
F = k * q1 * q2 / L², where k is the coefficient 9 * 10 ^ 9, q1 is the value of the first charge, q2 is the value of the second charge, L is the distance between them.
3. Let us express the distance from this expression:
L = √ (k * q1 * q2 / F)
4. Substitute the numerical values:
L = √ (k * q1 * q2 / F) = √ ((9 * 10 ^ 9) * (7 * 10 ^ -9) * (9 * 10 ^ -6) / (3 * 10 ^ -3)) = 0.43 m.
Answer: Distance between charges L = 0.43 m