Description: A simple speaker made from a waxed paper cup, a small coil and a Nd-B-Fe magnet.

The coil consists of approximately 50 turns of #32 wire, wound on masking tape. A AA battery was used as the form. The hollow coil is epoxied into a hole in the base of the cup. Banana plugs allow connecting the coil to the headphone jack of the radio/cassette player. Plug it in and move the 1/2 inch diameter Nd-B-Fe magnet (held on a steel rod for ease of handling) into the coil. The sound is remarkably good. Observe the variation in intensity with position of the magnet.

Note that 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.

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

Cautions: Please handle the 'speaker' with care, the coil is easily destroyed.
The magnet is very strong and can be dangerous (shatter, or pinch fingers severely) if not handled with great care.

Concepts demonstrated: Lorentz force

Setup Time: Short.

Difficulty/Commitment: Straightforward

Visibility: Apparatus is small. Video will be required in large halls if it is desired to show the details of the construction.

Related demonstrations:

References: PIRA 5H40.??
From the article "Drinking Cup Loudspeaker - A Surprise Demo" by Peter Heller, The Physics Teacher 35, 334 (Sept 1997).
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