Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Coulomb's Law

The electric force acting on a point charge.

coulombs law - force

Coulomb's law calculates the electric force acting between to electric charges q1 and q 2and can be expressed as

F = k q1 q2/ r2

= q1 q2/ (4 π ε0 r2)    (1)


F = force of attraction or repulsion (N)

k = Coulomb's constant = 1 / (4 π ε0 ) = 8.9875517873681764 × 109 (Nm2/C2) in air

q = charge (Coulombs, C)

r = distance between charges (m)

ε0 = permittivity of space or vacuum

The quantity of charge (number of electrons) is measured in the unit Coulomb - C - where

1 coulomb (C) = 6.24 1018 electrons

The smallest charge that exists is the charge carried by an electron equal to -1.602 10-19 coulomb .

Example - Force between two Charged Bodies

Two spheres in air with distance 20 mm is both charged with 2 μC (2 10-6 C) . The force acting between the two spheres can be calculated as

F = ( 8.98755 109 Nm2/C2) ( (2 μC ) (10-6 C/ μC )) ( (2 μC ) (10-6 C/ μC )) / ((20 mm)(10-3 m/mm))2

= 90 N

Related Topics

  • Electrical

    Electrical engineering with units, amps and electrical wiring. Wire gauges, electrical formulas, motors and more.

Related Documents


Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .


This page can be cited as

  • The Engineering ToolBox (2013). Coulomb's Law. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter