Explain the Electrostatic force between 2 charges

A point charge Q1 = +5.0 x 10-7 C. What is the magnitude and direction of the electrostatic force on each of them? The charges are situated in dry air.
Solution.
This the simplest possible problem. We only need to substitute given values into the Coulomb law.

For dry air k = 8.99x10⁹ Nm²/C². After substituting numbers

F= -53940.0 x 10^-4 N = -5.39 N.

The magnitude of the force is the same on both charges. It is in accordance with Newton’s third law of motion. The force between charges of different signs attracts these charges, therefore the force on Q₁ is directed towards Q₂ and vice versa.