Concepts

Faraday's law, Lenz' law, magnetic fields from currents

Overview

A magnet falling down a copper tube is slowed by magnetic fields from eddy currents induced in the tube. A magnet falling down a glass tube is unaffected.

Details

Equipment

• [2] Lab stand
• [1] Glass tube
• [1] Copper tube
• [2] 3-finger clamp
• [4] 90-degree clamp
• [2] Bell
• [1] Aluminum slug
• [1] Magnet
• [1] Plastic container

Classroom Assembly

1. Set up lab stands, each with a 3-finger clamp holding a tube and a bell mounted just below the tube.
2. Put the plastic container under the bells to catch the magnet and slug when they fall.

Script

1. Using either the document camera or overhead projector, show the class that the aluminum slug and magnet are the same diameter.
2. Put the aluminum slug through both tubes, showing there are no obstructions inside. The bells will ring when the slug hits them.
3. Put the magnet through the glass tube, showing how it falls as the aluminum slug did.
4. Put the magnet through the copper tube. In about 8 seconds, it will make a very light "ding" sound on the bell.

Additional Resources