How does a homopolar motor work

Homopolar Motor - The simplest motor in the world / Curiosities / Homopolar Motor

A small instruction manual on how to build a DC motor yourself.

What is needed

Few parts are needed to build a homopolar motor. You can find these in every craft kit:

  • Wood screw
  • Battery (Mignon or larger)
  • A round neodymium magnet (available on Amazon or Ebay)
  • A piece of cable (approx. 10 long, stripped at both ends)


The head of the screw is placed in the middle of the magnet. The battery is held with the tip pointing straight down. The screw with the magnet is attached to the tip of the battery. One end of the stripped cable is now pressed against the flat end of the battery with a finger.

It spins

The other end is now carefully held on the magnet with the other hand. The magnet starts to turn!

In the second part of the following video, another type of engine is shown. A correspondingly bent wire rotates around the battery:

The direction of rotation can be reversed by turning the magnet or the battery.

How does the homopolar motor work?

The driving force is, in the truest sense of the word, the Lorentz force. If a current-carrying conductor is in a magnetic field, it is acted on by a force transverse to the magnetic field and to the current flow.

A more detailed physical consideration can be found here:
Seán M. Stewart - Some simple demonstration experiments involving homopolar motors


Incidentally, the idea of ​​the homopolar motor is not entirely new. In fact, it was the first device that could produce rotation using electromagnetism. The engine was presented to the Royal Institution of Great Britain by Michael Faraday in 1821.