Electric Force Between Charges

A French scientist, Charles Coulomb, investigated the nature and magnitude of force between charges and came out with his findings known as Coulomb’s law.

Coulomb’s law states that the force [F] of attraction or repulsion between two charges is directly proportional to the product of their charges q₁ and q₂ and inversely proportional to the square of the distance between them.

The electrostatic force can be repulsive (between two positive or two negative charges), or attractive (between a positive and a negative charge). This force is a direct consequence of the electric field created by a charge. This field is directed toward a negative charge and moving away from a positive charge.

Protons have a positive charge. Electrons have a negative charge. The charge on the proton and electron are exactly the same size but opposite.

Coulomb's law can be expressed mathematically as:

\( \scriptsize F \propto \normalsize \frac{1}{r^2}\)....(1)

\( \scriptsize F \propto q_1 q_2\)......(2)

Combining (1) and (2):

\( \scriptsize F \propto \normalsize \frac{q_1 q_2}{r^2}\)

This can be expressed as:

F = \( \scriptsize K \normalsize \frac{q_1 q_2}{r^2}\)

Where K = constant of proportionality

K = \( \frac{1}{4 \pi \varepsilon_0} \scriptsize = 9.0 \: \times \: 10^9\: Nm^2 C^{-2}\)

\( \scriptsize \varepsilon_0 \)= permittivity of air or free space =  8.85 × 10^-12 Fm^-1

Materials with high permittivity allow current to pass through