Concepts

Lorentz force

Overview

A drinking cup, a small coil, and a magnet are turned into a loudspeaker.

A cup with a hole and a second coil are provided to allow demonstrating the construction of the speaker.

Details

Equipment

• [1] Waxed paper cup
• [1] Small coil
• [1] NdBFe magnet mounted on a rod
• [1] Radio
• [1] Banana cable
  
• [1] 3.5 mm plug adapter
• [1] Camera

Important Notes

• Please handle the 'speaker' with care. The coil is easily destroyed.
• The magnet is very strong and can cause injury (by pinching, shattering, etc.) if not handled with great care.
• The speaker action depends on the radial component of the field from the magnet. In a conventional speaker the magnet would sit in a permeable cup.
• In large lecture halls, use a camera to show the details of the construction.

Script

1. Turn on the radio and tune in to a radio station.
2. Connect the banana plugs to the 3.5 mm adapter and the 3.5 mm adapter to the headphone jack of the radio.
3. Move the magnet into the coil.
4. Move the magnet in and out of the coil, noting the variation in sound intensity as the position varies.

Additional Resources