Ring Shooter (Lenz's Law Apparatus)

Homemade apparatus

Commercial apparatus

These are available commercially under the name of Lenz's Law Apparatus. You can also make one cheaply.

This is a classic demonstration of electromagnetic induction. The alternating current produces a changing magnetic field in the coil. That, in turn, induces eddy currents in the aluminum ring, which cause a magnetic field that opposes (Lenz's Law) that of the core. The ring is shot off.

The core is made of pieces of steel coat hangers. A solid core would lose too much energy in eddy currents.

Insulated copper wire is wound around the core. You might experiment with the number of windings.

Have a metal shop cut an aluminum or copper ring. You want the ring to be non-magnetic metal and lightweight. Cut another ring of the same material, but cut a slit. Current cannot flow in it, so no magnetic field is produced.

Also, use liquid nitrogen to cool the ring. What effect will that have?

Accelerated Particles: Copper or aluminum ring

Accelerating Propellent: Induced magnetic fields

Detectors: Eyes

Variables to Investigate

• Number of wire windings
  
• Solid or wire core
  
• Different metals for ring
  
• Solid or cut ring
  
• Effect of temperature of the ring

Safety:

• Don't stand over the apparatus, as the ring can be projected 2-3 meters high, with great force.
  
• The ring will get hot, especially if you hold it down.

Problems—Limits to analogy:

• Acceleration is not continuous but one-time.
  
• Collisions are not possible nor useful.

RATINGS Excellent Good Acceptable Marginal Yuk EASY CONSTRUCTION COST DRAMA QUANTITATIVE

RESOURCES AND CONTACTS Resources All science catalogs sell this apparatus under the names of ringshooter, Lenz's Law apparatus, jumping ring, etc. Contacts: Ken Cecire built one recently.

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