Electricity · Physics

Forces between charges follow a clear inverse-square law.

Coulomb’s law gives the magnitude and direction of electric force between point charges. Superposition then turns many-charge problems into structured vector addition.

This topic

Coulomb’s Law

Use Coulomb’s law as a vector law, apply superposition, and compare electric forces to gravitational forces.

Law

Mathematical form and meaning

Coulomb’s law gives the force between point charges separated by a distance r. The magnitude follows an inverse-square dependence, and the sign determines attraction or repulsion.

Inverse-square dependence on separation
Attraction vs repulsion by charge sign
Point-charge assumption and when it is reasonable
Unit awareness and scaling intuition

Vector

Vector nature of electric force

Electric force is a vector pointing along the line joining the charges. Correct solutions require a clean geometry picture and a consistent sign convention.

Direction along the line of centers
Choosing coordinate axes for components
Sign conventions that avoid confusion
Symmetry checks for sanity

Method

Superposition principle

Net electric force is the vector sum of forces from each source charge. Superposition is simple to state and easy to misuse unless you add vectors carefully.

Add forces one source charge at a time
Use components for non-collinear forces
Symmetry shortcuts when geometry permits
Common mistakes: adding magnitudes only

Perspective

Comparison with gravity

Coulomb’s law mirrors Newton’s law of gravitation in form, but electric forces can attract or repel and are typically far stronger at the particle scale.

Same inverse-square structure
Electric: two signs; gravity: always attractive
Relative strength and what it implies
When gravity dominates (macroscopic neutrality)

Practice

Practice & Exercises

Practice computing forces, resolving components, and applying superposition in multi-charge configurations.

Two-charge force magnitude and direction
Component-based superposition drills
Symmetry-based setups (line, triangle, square)
Concept checks: attraction/repulsion and scaling
Exam-style Coulomb’s law sets