Physics·Electrostatics

Coulomb's Law Simulator

Drag charges around the field. Watch the force vectors and field arrows update.

ForceField

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Charges (2)

Show electric field vectors

Coulomb's law is the electrostatic analog of Newton's law of gravitation: two point charges attract or repel with a force proportional to the product of their charges and inversely proportional to the square of the distance between them. Drag the charges below to move them. Change the sign or magnitude with the controls. The arrows in the background show the electric field; the red arrows show the force on each charge.

Key equations

Force between two charges

$F = k\dfrac{|q_1 q_2|}{r^2}$

Coulomb's constant

$k = 8.99 \times 10^9 \, \text{N·m}^2/\text{C}^2$

Electric field of a point charge

$\vec{E} = k\dfrac{q}{r^2}\,\hat{r}$

Force on a test charge

$\vec{F} = q\vec{E}$

Key ideas to remember

1
Like signs repel, opposite signs attract — the force vector always lies along the line joining the charges.
2
The field of a point charge falls off as $1/r^2$ ; the potential falls off as $1/r$ .
3
Superposition: total field is the vector sum of contributions from every charge.
4
A dipole (equal and opposite charges close together) produces a distinct 'figure-eight' field pattern.

Coulomb's Law Simulator

Key equations

Key ideas to remember

Related topics

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