One way to imagine magnetic fields is by drawing lines showing the direction a compass would point if placed into the field. Here’s an example:
The black lines depict the magnetic field directions. This can be hard for students to understand at first, so another technique is to show the field lines by placing iron filings near a magnet and watching them align themselves in the direction of the field, like this:
The black bar is the magnetic. These sorts of demonstrations can be artistic:
And given enough filings can even show the field in 3D:
But the best illustrator of the field, in my opinion, is to show the effect of the field on a liquid. ‘Ferrofluid’ is the name of a magnetic liquid invented in 1963 that suspends micron-sized iron nanoparticles in a viscous fluid. This allows them to flow as if they are a liquid, and leads to striking displays of magnetic fields like this:
The magnet in the above picture is underneath the bowl containing the ferrofluid.
I’ve been using images like all of the above in class for years when I introduce the magnetic field and when I found out last week how easy it was to actually purchase ferrofluid (which is toxic and can apparently stain anything) I just jumped at the chance. Here’s what my new bottle of ferrofluid looks like:
Just some black oil in a bottle isn’t it? The bottle is filled, most likely with pure water. The fluid is likely oil filled with the iron nanoparticles, and is extremely viscous and doesn’t mix with the water. It’s quite unremarkable by itself, but becomes something quite special when exposed to a magnetic field.
Here’s a short video I just made (it’s in HD, so fullscreen it if you like):
Wonderful isn’t it? This will stay in my office with all my other demonstration units, and I’m sure it will give students and my coworkers many smiles!
This is so cool!