Experiments with magnets and our surroundings

Magnetic fields

Single bar magnet

The field you see above is a rough calculation of the field around a single magnet.
Its North pole is at the top.

Let's review this in further detail.  What I'll present are the fields around a single magnet, pairs of magnet in various positions, and combinations of magnets such as in some of the experiments demonstrated on other pages of this site.

In order to be consistent, we have stated that the North pole of a magnet will be the end of a magnet that is attracted to the magnetic pole that is located in Northern Canada.  We also state that the field lines flow in a particular direction - they leave the North pole of a magnet, travel through the air or other things and enter the South pole of the magnet.  Inside the magnet, the field lines travel from the South pole to the North pole where they will exit again.  They travel in closed loops.  These loops don't start or stop at any point, nor do they cross other loops.  When the field lines are close together, the magnetic field is strong.  When the field lines are far away from one another, the magnetic field is weak.  A unit of measure of the strength of the magnetic field is the Gauss or the Tesla. 

So, let's look at some field lines and magnetic fields around various magnets.  For these diagrams, I used a small arrow inside the magnet to show the direction of the magnetic field lines.  The head of the arrow would be pointing to the North pole of the magnet and away from the South pole of the magnet.

Bar Magnet

This shows the field lines around a long bar magnet.  The North pole is at the right.

This shows the magnetic field strength around the bar magnet.  The darkest blue is the weakest field.  As the color goes to green and yellow and red, the field becomes stronger.  It is strongest in the corners, not in the center of the poles!  The magnetic field is weakest along the surface in the middle of the side of the magnet.

This is a close-up of the field at the North pole.  Notice how the field bends as it exits the magnet.

This is a close-up of the magnetic field strength at the North pole.  The colors are different for this to point out how the field is not maximum in the middle of the pole, but is stronger at the corners.  When farther from the pole, the field strength is maximum along the center-line of the pole.  Interesting?

Disk Magnet

This shows the field lines around a disk magnet where the North pole is at the top.

This shows the magnetic field strength around the disk magnet.  Again, it is strongest in the corners, not in the center of the poles!  The magnetic field is weakest in the middle of its poles!  If you are wondering, this picture and the one like it for the bar magnet are almost identical, but are slightly different.

If you were to put a BB onto one of the poles of this magnet, it would not want to stay in the middle of the pole, but would rather move to the edge where the field is stronger.