Coulomb’s Law (Electric Force) (Also seen in GCSE Physics 2)
The electrostatic force acts between all charged particles and can be attractive or repulsive. It is the charges themselves that cause the force to exist. The force that acts between two charges, Q1 and Q2, whose centres are separated by a distance of r is given by:
Like charges Opposite charges Like charges
The proportional constant was found and the equation becomes:
ε0 is the Permittivity of Free Space, ε0 = 8.854 x 10-12 F m-1
When one of the charges is large, Q, the force between it and a test charge, q, whose centres are separated by a distance of r is given by:
If the two charges are positive, (+Q)(+q) = + Qq A positive force means the charges repel.
If the two charges are negative, (–Q)(–q) = + Qq A positive force means the charges repel.
If one is negative and one is positive, (–Q)(+q) = – Qq A negative force means the charges attract.