Coulomb's Law Calculator

This calculator computes the electrostatic force between two point charges using Coulomb's Law, one of the fundamental laws of physics. Enter the magnitude of each charge in microcoulombs and the distance separating them in metres, and the calculator returns the force in newtons and indicates whether it is attractive or repulsive. It also shows the electric field strength at the location of the second charge due to the first. Coulomb's Law was established experimentally in the 1780s and states that the force between two point charges is proportional to the product of their charges and inversely proportional to the square of the distance between them: F = k x q1 x q2 / r squared. The constant k is Coulomb's constant, approximately 8.988 x 10 to the 9 newtons metres squared per coulomb squared. It is related to the permittivity of free space by k = 1 / (4 x pi x epsilon_0). When both charges carry the same sign, the force is repulsive: the charges push each other apart. When the charges carry opposite signs, the force is attractive: they pull each other together. The magnitude of the force is the same regardless of direction. The coulomb is a large unit of charge; in practice most problems involve microcoulombs (10 to the minus 6 C) or nanocoulombs (10 to the minus 9 C). This calculator accepts charge input in microcoulombs for convenience, which covers most physics textbook problems. For charges of opposite sign the calculator still shows the magnitude of the force and labels it attractive. Enter positive values for positive charges and negative values for negative charges.

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k = 8.9875 x 10^9 N m2/C2. Coulomb's Law applies to point charges in a vacuum or air. For charges in a medium, divide k by the relative permittivity of the medium.