Coulomb's Law

Key Stage 5

Coulomb's Law states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Coulomb's Law can be used to calculate the magnitude of the force acting between two charged point particles.

Coulomb's Law has a similar form to Newton's Law of Universal Gravitation in that both are given with a constant multiplied by a product of some physical property (charge and mass) and inversely proportional to the square of the distance between particles.

\(F=\dfrac{1}{4 \pi \varepsilon_0} \dfrac{q_1q_2}{r^2}\)

Where;

\(F\) = The force acting between the charged particles

\(\varepsilon_0\) = The Permittivity of Free Space (\(8.85\times10^{-12}Fm^{-1}\))

\(q_1\) = The charge on one particle.

\(q_2\) = The charge on the other particle.

\(r\) = The distance between the particles.

The definition can be derived from the equation by considering;

\(\dfrac{1}{4 \pi \varepsilon_0}\) is a constant so the left hand side and right hand side are proportional.

\(q_1q_2\) is the product of the charges.

\(\dfrac{1}{r^2}\) is the the inverse of the square of the distance.

Therefore;

\(F\propto\dfrac{q_1q_2}{r^2}\)