Solve electrostatic force, one missing point charge, or separation distance for two point charges using Coulomb's law, with attraction-versus-repulsion context and charge-product checks.
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Basic circuits
A Coulomb's law calculator translates two-point-charge problems into an actionable force, missing charge, or separation result without reworking the inverse-square algebra each time. This version solves electrostatic force directly, or back-solves one missing variable while keeping the attraction-versus-repulsion interpretation visible.
This page solves the force between two point charges, or solves one missing quantity among force magnitude, one charge, or separation distance when the other three values are known.
That makes it useful for electrostatics examples, first-pass field intuition, and quick checks where unit normalization and sign interpretation are just as important as the raw number.
Coulomb's law scales linearly with the product of the two charges and falls with the square of the separation. Doubling one charge doubles force magnitude, while doubling the distance cuts force magnitude to one quarter.
This calculator preserves the sign of the charge product in force mode so you can immediately tell whether the interaction is attractive or repulsive.
F = k × q1 × q2 / r²
Point-charge force is proportional to the charge product and inversely proportional to distance squared.
When you solve for a missing charge, the entered force is treated as a magnitude and the calculator reports the solved charge magnitude with explicit polarity context. That keeps the algebra stable even when the other known charge is negative.
The distance solver similarly uses the magnitude of the charge product so opposite-charge cases still return a valid physical separation rather than failing on a negative radicand.
q = F × r² / (k × |q_other|)
Rearranging the force equation isolates one missing charge magnitude from the known force, distance, and other charge.
r = √(k × |q1 × q2| / F)
Distance follows from the inverse-square relationship when the charge magnitudes and force magnitude are known.
This calculator assumes two ideal point charges in free space. It does not model dielectric media, distributed charge geometry, shielding, or many-body interactions.
Use it as a planning and educational reference. If the real problem depends on geometry, materials, or field integration, move to the method that captures those effects explicitly.
Frequently asked questions
Because the distance solve uses force magnitude and charge-product magnitude. The attraction-versus-repulsion interpretation is still reported, but the square-root step uses the physical magnitudes needed for distance.
A negative signed force indicates attraction because the two charges have opposite signs. A positive signed force indicates repulsion from like charges.
Only as a rough first-pass estimate. Real objects often have distributed charge, geometry effects, dielectric surroundings, and shielding that this point-charge model does not include.
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