Homopolar motor. Photo Credit: leventsakar.net

Electric motors are used in many applications from robotics to children’s toys.  Although many of these motors are DC motors, Homopolar motors are the simplest of motors and are easy to show students in a classroom setting.  All it takes to build your first simple motor are three common materials you can probably find around the house: copper wire, a AA battery, and neodymium magnets.

Common heart shaped approach. Photo Credit: electronics-micros.com

Constructing the motor is simple but getting it to work can take trial and error as well as a bit of patience.  Here’s how to do it:

1) Attach the magnet to the negative side of the battery.
2) Strip the copper wire completely or for safety, in the middle and at the two ends.
3) Bend the wire so that one end touches the positive terminal and the other end touches the magnet.  A common approach is a heart shaped wire for better stability.
4) Watch: As the copper wire touches the magnet, the wire will begin to spin.

Current (blue) flows from the positive terminal to the magnet at the negative terminal. The current flows in the presence of a magnetic field (red). This causes a force perpendicular to those directions (in the page on the left of the battery and out of the page to the right of the battery). This force causes the wire to spin. Photo Credit: Physics Central

How does it work?  Well the theory can get as detailed as you want it to be but to keeps things simple, I will explain the homopolar motor briefly.  The copper wire connects the positive terminal to the magnet at the negative terminal.  This completes the circuit, allowing current to flow through the circuit (and the wire).  Due to the magnet, the current is flowing in the presence of a magnetic field around the battery.  When current flows in a magnetic field, it will experience a force called the Lorentz force.  This force acts perpendicular to  the magnetic field and the flow of the current (and the wire).  Consequently, the perpendicular force pushes the wire around the battery.

Once you get a working motor, you can change the shape of the wire to any shape you want!  Have fun!

Until next time…