This week with Form 6 it was Magnetic Fields.
One of the concepts I try to emphasise is that this is a 3-dimensional phenomena, as opposed to the 2-dimensional pattern that you get from sprinkling iron filings on a page.
Some of these help:
I got the ferrofluid from teachersource.com
For bonus points, on this next video can you guess why the clips are only standing up sometimes as opposed to all the time?
And no discussion on Magnetism could be complete without a mention of the man who gives his name to the unit of Magnetic Field Density; the Tesla.
All these links are available from the Magnetism page of the website.