Coulomb's Law Calculator
Electric force between two point charges — with attraction/repulsion classification.
Formula
F = k · |q₁·q₂| / r²
k = 1/(4π·ε₀·εᵣ), ε₀ = 8.854×10⁻¹² F/m in vacuum.
Sign of q₁·q₂ tells you attraction (−) vs repulsion (+).
k = 1/(4π·ε₀·εᵣ), ε₀ = 8.854×10⁻¹² F/m in vacuum.
Sign of q₁·q₂ tells you attraction (−) vs repulsion (+).
Physics behind Coulomb's law
Coulomb's law is the electrostatic analogue of Newton's universal gravitation — both are inverse-square laws. The force drops as 1/r², so doubling the distance reduces the force by a factor of four. Unlike gravity, the electric force can be attractive or repulsive depending on the sign of the charges. The constant k is enormous (≈9 × 10⁹ N·m²/C²), which is why even tiny charges at short distances produce noticeable forces.
Worked example
q₁ = 1 μC, q₂ = −1 μC, r = 5 cm, vacuum
F = 8.988×10⁹ · (10⁻⁶·10⁻⁶) / 0.05² = 3.595 N (attractive)
Related tools
FAQs
What is Coulomb's law?
F = k·q₁·q₂/r² for point charges.
What is k?
About 8.988×10⁹ N·m²/C² in vacuum.
When is the force attractive vs repulsive?
Opposite charges attract; like charges repel.