Coulomb's Law Calculator
Enter two charges and the distance between them to find the electrostatic force with Coulomb's law, and see whether the charges attract or repel.
How to use the Coulomb's law calculator
- Enter the first charge in coulombs, using a value like 1e-6 for one microcoulomb.
- Enter the second charge, including a minus sign for a negative charge.
- Enter the distance in metres and read the force, plus whether it attracts or repels.
Examples
Two like charges
q1 = 1 uC, q2 = 1 uC, r = 1 m
F = 8.99e-3 N, repulsive
Opposite charges
q1 = 1 uC, q2 = -1 uC, r = 1 m
F = 8.99e-3 N, attractive
Frequently asked questions
What is Coulomb's law?
Coulomb's law gives the force between two point charges as F = k x |q1 x q2| / r^2, where k is about 8.9875 x 10^9 N m^2 / C^2 and r is their separation.
When is the force attractive or repulsive?
Charges with opposite signs attract, and charges with the same sign repel. The calculator reports which case applies from the signs you enter.
What units should I use?
Charge in coulombs and distance in metres give the force in newtons. Enter microcoulombs as a value like 1e-6 and nanocoulombs as 1e-9.
Why must the distance be greater than zero?
The force varies as 1 / r^2, so a zero distance would be infinite and non-physical. The calculator rejects a zero or negative distance.
How does this compare to gravity?
Coulomb's law has the same inverse-square form as Newton's law of gravitation, but the electrostatic force is vastly stronger for typical charges.
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