Coulomb’s Law Calculator
Find the electrostatic force between two point charges from their charges and separation using Coulomb’s law.
How it works
F = k·|q₁·q₂| / r² · k = 8.988×10⁹ N·m²/C²
Coulomb’s law gives the force between two point charges: it grows with the product of the charges and falls off with the square of the distance between them, just like gravity. Like charges (same sign) repel and opposite charges attract, so the sign of the product tells you the nature of the force. Because k is enormous, even microcoulomb charges a few centimetres apart produce forces you can measure by hand.
Worked example
Charges of +1 µC and −2 µC set 0.05 m apart: F = 8.988×10⁹ × (1×10⁻⁶ × 2×10⁻⁶) / 0.05² = 8.988×10⁹ × 2×10⁻¹² / 0.0025 ≈ 7.19 N of attraction.
Sources: Coulomb’s law — Wikipedia
Frequently asked questions
When is the force attractive versus repulsive?
Opposite-sign charges attract, like-sign charges repel. Enter the charges with their signs; the calculator reports the magnitude of the force and whether it pulls the charges together or pushes them apart.
Why does distance matter so much?
The force follows an inverse-square law: double the separation and the force drops to a quarter; triple it and the force falls to a ninth. Small changes in distance change the force dramatically.
What is a microcoulomb?
A microcoulomb (µC) is one millionth of a coulomb, 10⁻⁶ C. Everyday static charges are in this range, so the inputs use µC and are converted to coulombs internally.
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