Coulomb's Law
The force between two point charges: the formula, the constant, a worked example, and how it compares with gravity at the same distance.
Questions people ask
Why is a coulomb such a large unit?
Because it was defined from the amp, which is a practical circuit quantity. Two 1 C charges a metre apart would repel with nearly nine billion newtons — nothing in static electricity comes close.
Does Coulomb's law work inside a material?
The form holds, but the constant changes. Dividing by the material's relative permittivity accounts for it — water weakens the force by a factor of about 80.
Does this page work offline?
Yes, after the first visit. The service worker caches it, so the reference stays available with no connection.
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Last updated 22 August 2026