Equipment: A compass, iron filings, a current carrying solenoid and a 40 Amp power supply.

What it does: The compass shows the direction of the field lines in and around the solenoid. The iron filings line up along the field lines.

Concepts Demonstrated: The magnetic field lines around a solenoid.

Classroom assembly:

1. Place the solenoid on the overhead projector and focus the projector on the Plexiglas platform.
2. Connect each terminal of the solenoid to the power supply.
3. Place the compass at various locations in and around the solenoid.
4. Press the black power button on the front of the power supply and hold while you discuss the compass reaction.
5. Remove the compass.
6. Sprinkle iron filings evenly in and around the solenoid.
7. Press the black power button on the front of the power supply and hold.
8. Tap the Plexiglas frame with your knuckles, a screwdriver or a similar implement to help the iron filings 'jump' to the magnetic field lines.
9. Release the power button.
10. When finished, shake the iron filings onto a piece of paper and replace in the iron filing shaker.

• Compass polarities can be reversed. Bring spare compasses. Undamped compasses work best for this demo.
• The contacts are critical. If the demo is not working properly, loosen the contacts on the power supply and retighten.
• The power button on the power supply can weld open. Always use a power bar that can be shut off manually if this occurs.
• The Plexiglas platform will not focus on all overhead projectors. Ensure the demo will work on your classroom overhead projector in advance.

Cautions: The solenoid becomes hot over time and the power button on the power supply can weld open. Do not turn on for longer than necessary.

Setup Time: Medium.

Difficulty: Straightforward.

Visibility: High. This demonstration can be shown on the overhead projector and is appropriate for large lecture halls.

Related demonstrations:

References:

Original Construction: Purchased