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Interaction of Point Charges
Charles de Coulomb found the law of interaction of point charges in 1784 through experimentation. In SI Coulomb's law can be expressed as

F = (1/4πε0)(q1q2/r2) ,

Where ε0 = 8.85*10-12C2/Nm2 is an electric constant, q1 and q2 are the magnitudes of point charges, and r is the distance between them. The direction of the vector force F is along the line that connects the charges. If the signs of q1 and q2 are the same (F > 0) , the force is that of repulsion, and if they are opposite (F < 0) , the force is that of attraction.

The interaction of electric charges that are at rest is called electrostatic.

Note that electrostatic interaction satisfies the principle of superposition.
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