Calculadora da Lei de Coulomb
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
F = k·q₁·q₂/r²
About this calculator
The Coulomb's Law Calculator determines the electrostatic force between two point charges. It uses the formula F = k·q₁·q₂/r², where F is the force in newtons, k is the electrostatic constant (approximately 9×10⁹ N·m²/C²), q₁ and q₂ are the charges in coulombs, and r is the distance in meters. The calculation is performed automatically based on user inputs.
This calculator is useful in educational settings, such as high school and college physics classes, as well as practical applications in electrical engineering. For instance, when designing circuits or analyzing interactions between charged particles, you can quickly estimate the force magnitude. It handles both positive and negative charges, indicating attraction (opposite signs) or repulsion (same sign).
Important considerations: ensure consistent units (coulombs for charge, meters for distance). The formula assumes point charges, i.e., bodies with negligible size compared to the distance between them. In real scenarios with multiple charges, the net force is the vector sum of individual forces. This calculator solves only the two-charge case.
Frequently asked questions
What does the calculator return if the charges have opposite signs?
The force will be negative, indicating attraction between the charges. The negative sign is a convention to represent the direction of the force.
Can I use units like microcoulombs or centimeters?
Not directly. Convert charges to coulombs (1 µC = 1×10⁻⁶ C) and distance to meters (1 cm = 0.01 m) before entering values.
Does the calculator consider the medium between charges?
No. The formula assumes vacuum. For other media, replace k with k/ε_r, where ε_r is the relative permittivity of the material.
What is the exact value of the constant k?
k = 8.9875517923×10⁹ N·m²/C². The calculator uses 9×10⁹, which is a sufficient approximation for most calculations.
Can I use it to calculate the force between more than two charges?
No. This calculator solves only the pair of charges. For multiple charges, calculate the force between each pair and add vectorially.