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Coulomb's law
Beginner
Force between point charges.
F = kq₁q₂/r²The force between two point charges is F = kq₁q₂/r², along the line joining them, repulsive if like, attractive if unlike.
Two 1 μC charges 10 cm apart: 0.9 N.
Use the magnitudes for the size and signs for direction.
In more detail
Coulomb's law gives the force between two point charges, F = kq1q2/r². Like charges repel, unlike charges attract, and the force acts along the line joining them.
Real-world uses
- Designing electrostatic devices and calculating forces between charged particles.
- Explaining why atoms bond through electrical attraction.
- Engineers designing insulators and clean rooms use Coulomb's law to estimate the force between charged particles.
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Frequently asked questions
Is Coulomb's law like gravity?
Both fall off with inverse square, but electric forces can attract or repel, while gravity only attracts.
What if the charges are moving?
Coulomb's law applies to static charges, and moving charges also produce magnetic forces.
Why do like charges repel?
Two positive or two negative charges push each other apart, while opposite charges attract.
Related topics in Electrostatics
Charging by friction, contact, induction · Conservation of charge · Quantisation of charge · Coulomb constant · Superposition of forces · Electric field