Electromagnetic Ring Tosser: Magnetic Levitation Using Induction

The Idea

This is a fun demo with somewhat surprising results. You will use a powerful magnetic field to exert a force on a material that is not normally magnetic. You will generate a circulating current using electromagnetic induction. The result is that the magnetic repulsion causes a metal object to be forcefully thrown into the air.

What You Need

• ring launcher apparatus (Elihu Thomson apparatus). Pictured in Figure 105-1 is PASCO EM-8661.
• copper collar
• aluminum ring
• split aluminum ring
• copper ring



• lead ring
• coil of insulated wire connected in series with a low-wattage light bulb
• AC voltmeter (or multimeter configured as an AC voltmeter)
• tongs
• optional: Pyrex bowl with liquid nitrogen

Method

1. Safety: All wiring to the launcher should be appropriately enclosed and insulated to avoid a potential shock hazard. Without giving away the results of this experiment yet, it should come as no surprise that metal objects will be launched, sometimes at significant velocities. Make sure no one and nothing of value can be hit by flying rings. Caution should be exercised when working with low-temperature rings. Avoid constraining any of the collars for any prolonged period, which could result in elevated temperatures and burning hazard. The current should flow through the coil of the launcher for a limited time. Be careful to avoid overheating the coil by flowing current for an excessive time.
2. Slide the aluminum ring over the iron core of the ring launcher apparatus and slide in down over the coil.
3. Activate the launch switch for a few seconds to apply 120V alternating current to the coil.
4. Repeat with the other rings and collars.
5. Connect an AC voltmeter across the two sides of the split ring to measure the current while the current is flowing in the core of the launcher. Similarly, put a coil of wire around the core. Compare the AC voltage developed in one, two, or multiple coils of wire.
6. Place the coil of wire attached to the light bulb over the launcher coil and apply current to the launcher, as shown in Figure 105-2.
7. Hold the copper ring over the collar for a few seconds with the launcher turned on and feel the collar's temperature. (Be careful not to hold it too long or it may get too hot to handle.)
8. For this next part, make sure the ceiling is high enough. Immerse the rings in liquid nitrogen and activate the launcher.

Expected Results

Closed conductive rings and collars will be throw vertically by the ring tosser, as shown in Figure 105-3. The copper ring is thrown the highest, followed by aluminum. The copper collar is raised, but it is more sluggish. The split rings are not lifted. An AC voltage of a few millivolts can be measured across the split ring. A ring that is held down while the current is flowing in the coil will heat up significantly. The rings cooled in liquid nitrogen are much more response than their room temperature counterparts. The cooled copper ring will fly the highest and can likely damage a standard 8 to 10 foot (2 meter) ceiling. The light bulb will be illuminated when held over the current-carrying coil.

This article is brought to you by: