Plotting Magnetic Field Lines

A simple experiment demonstrating how iron filings may be used to plot field lines around:
A single magnet
Two magnets (repelling)
Two magnetic (attracting)
A current carrying wire
A current carrying solenoid (a long coil)

The basic technique is:
Cover the magnets with paper (or place paper in the area you will be scattering the filings)
Gently shake a few iron filings on to the paper.
Tap the paper gently to help the iron filings settle into a pattern.

The field line for the current carrying wire are very faint and difficult to see. This is because the field that is produced is very weak. If you look carefully, though, you may be able to make out some concentric circles going around the wire.