Electromagnetism
Coulomb's Law Calculator
Calculate the electrostatic force between two point charges, or solve for charge or distance. Attractive vs repulsive detection.
Result
F = kq₁q₂/r²
Step-by-Step Solution
What is Coulomb's Law?
Coulomb's Law describes the electrostatic force between two point charges. Like charges repel; opposite charges attract. The force is proportional to the product of the charges and inversely proportional to the square of the distance between them — exactly analogous in form to Newton's Law of Gravitation.
F = kq₁q₂/r²
k = 8.9875×10⁹ N·m²/C² | q₁, q₂ = charges (C) | r = distance (m) | F = force (N)
💡 Coulomb's constant k = 1/(4πε₀) where ε₀ = 8.854×10⁻¹² F/m is the permittivity of free space. In a medium, replace k with k/ε_r where ε_r is the relative permittivity.
Real-World Applications
Atomic Structure
Coulomb's Law explains why electrons are attracted to the nucleus and why heavier atoms have stronger nuclear binding.
Capacitors
Parallel plate capacitors store energy in the electric field between opposite charges on each plate.
Laser Printers
Electrostatic forces precisely direct charged toner particles onto paper to form text and images.
Ionic Bonds
Chemical bonds in salt (NaCl) form because Na⁺ and Cl⁻ are attracted by Coulomb's electrostatic force.
Frequently Asked Questions
How is Coulomb's law similar to gravity?
Both follow an inverse-square law (force ∝ 1/r²) and both act between pairs of objects. However, gravity is always attractive while electrostatic force can be attractive or repulsive. The electrostatic force is ~10³⁶ times stronger than gravity.
What is the unit of charge?
The SI unit is the Coulomb (C). One electron carries a charge of −1.6×10⁻¹⁹ C. The Coulomb is defined in terms of the ampere: 1 C = 1 A × 1 s.
What is the Coulomb constant k?
k = 8.9875×10⁹ N·m²/C². It can also be written as 1/(4πε₀) where ε₀ = 8.854×10⁻¹² F/m is the permittivity of free space. In a medium other than vacuum, replace ε₀ with ε₀ × ε_r.