SUBJECT AREA: (Electricity and Magnetism)

MATERIALS:

Cow magnet or a $3 neodymium magnet (Source: Dowling Miner Magnetics Corp., Sonoma, CA. 95476, 1-800-MAGNET-1)

Copper, aluminum, or brass tubing with a diameter greater than the magnet.

Plastic tubing with a diameter greater than the magnet

OPTIONAL: Two thick pieces of aluminum, some card board and some ruber bands.

PROCEDURE:

1) Hold the plastic tube vertically and drop the magnet down the plastic tubing having the students keep track of the time it takes for the magnet to travel through the tube.

2) Next, show the students that the magnet does not visibly react to the outside of the copper, aluminum, or brass tubing.

3) Hold the copper, aluminum, or brass tubing vertically and drop the magnet down the tube. Have the students keep track of the time it takes for the magnet to travel down the tube. ( I like to start with the plastic tubing and work my way up to the thick copper pipe.)

4) Last, drop a non-magnetic object down the copper, aluminum, or brass tubing. Have the students keep track ofthe time it takes for the non-metalic object to fall through the tube.

OTHER SUGGESTIONS:

1) Experiment with tubing of different thickness and diameter. How will this affect the time it takes for the magnet to travel through the tube. Try overlappping tubes of varying diameter.

2) As an alternative to metal tubing, you may also use 2 flat pieces of aluminum with cardboard spacers for the magnet to travel between. This device can be held together with heavy duty ruber bands.

QUESTIONS:

1) What happens to the magnet as it travels through the copper, alluminum, brass, and plastic pipes? How does the magnets rate of travel differ with the different materials, diameters, and thicknesses of pipe?

2) Are the magnets attracted to the outside of the copper, alluminum, brass, or plastic tubing?

3) Is there a visible interaction between the foil and the magnet.

RATIONALE:

As the magnet falls through the tube the magnetic field around it is constantly changing. The changing magnetic field induces the flow of eddy currents through the copper, aluminum, and brass tubing. The eddy currents have a magnetic field of their own which opposes the fall of the magnet. This causes the magnet to fall more slowly.

APPLICATION:

1) Eddy currents are generated from transformers and often lead to power losses. This is prevented by using insulating glue between the thin strips of the transformer.

2) Eddy currents are also used to reduce oscillations in many mechanical balances.

*This experiment was taken from The Exploratorium "Science Snackbook."