Figure 1 – Magnetic field lines around a circular magnet

Figure 2 – Magnetic field lines around a cylindrical magnet

A plastic case with small iron rods inside square compartments provides a convenient way to show magnetic field lines on a document camera. When a magnet is placed on top of the case, the rods line up with its magnetic field. Pictures above illustrate how this simple device displays the magnetic fields of a cylindrical AlNiCo magnet (standing vertically and laying horizontally).

Materials:

• Plastic case with iron filings (one or two)
• Cylindrical magnet

Demo:

Place the cylindrical magnet vertically (figure 1) or horizontally (figure 2) on the plastic case to observe the magnetic field lines of the magnet from varying directions.

Explanation:

When The magnetic field emanating from the magnet will polarize the magnetic iron filings, aligning them along the magnetic field lines.

Notes:

A document camera works best to show this demo to large lecture classes, if available. Otherwise, the demo room can provide a video camera.

The iron filaments can get caught against the walls of the plastic container and not accurately depict the magnetic field lines; tap the container or move the magnet around to loosen them.