Which Pole Is North?

Identifying the North Pole of your magnets

Once our customers receive their box of shiny magnets, we're sometimes asked about how to find out which pole is which.  Here are a few easy methods to help figure it out.

What's a pole?

Every magnet has both a North and a South pole.  There are no magnets with only one pole (see magnetic monopoles).  With an axially magnetized disc magnet, for example, you could write a big N and an S on either round face with a marker.  The question is, which is which?

When magnets are used in magnetic therapy, the poles are often referred to as being positive or negative.  Generally, the South pole is termed positive, and the North negative.  This terminology probably stems from trying to model the H-field as analogous to an electric E-field of positive charges, which works under some circumstances.

Pole Identifiers

A D4X0-ND with a labeled BY084 magnet

You can find several types of Pole Identifiers available on the K&J Magnetics website.  The simplest to use is the Electronic Pole Finder.  Simply point the tip at one side of the magnet, press the button, and an LED will light to indicate the polarity, North or South.  On a production line, this is your best bet.  It works well, consistently, and avoids any confusion.

A less expensive option is the D4X0-ND magnet.  It has a small dimple on the North end of the cylinder, and can be used to identify the poles on unmarked magnets.  The North pole of one magnet will be attracted to the South pole of another -- just remember that opposites attract!

Compass #1 - Magnets on a String

If you don't have a pole identifier readily available, you can use a little science to find the North pole of your magnets.  Your magnet's North pole is attracted to the Earth's North pole.  Technically, the Earth is labeled backwards -- the geographic North pole is actually like the magnetic South pole of a magnet.

If you hang a small stack of magnets on a long thread, the magnets will freely rotate.  Hang up your 3 foot length of string on a stable platform, like an overhead light.  Once it stops wobbling, the North end should be pointing North.  If you know roughly which direction is North (the sun rises in the East), you'll find your magnet's North pole.

Compass #2 - The Floating Magnet

Water Compass with an axially magnetized cylinder magnet

A fun science project is to float a magnet on piece of Styrofoam.  The lightweight, floating platform gives the magnet a nearly frictionless surface to freely rotate on.  The north pole quickly becomes obvious -- plus it's neat to play with!  This is a great science project idea for kids.

Compass # 3 - A Magnet on Edge

Less interesting to build, but super simple: You can place a disc magnet on it's edge on a smooth surface.  If your magnet is sized right to balance this way, it will twist to point North.  Simple, but effective.