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Coulomb's law gives the force between two point charges. If a charge is experience force due to number of point charges then the force can be calculated using the superposition principle. According to this principle the resultant force on a charge is the vector sum of the forces acting due to all the other charges individually.
According to coulomb's law the magnitude of the force acting on test charge q, due to charge Q, is given by
Where the terms have their usual meanings ...
Problems on Coulomb's law for point charges and electric field due to charges and dipole.