Why It Works
This is a demonstration of electromagnetic induction based on an apparatus developed by the prolific inventor Elihu Thomson. A constantly changing magnetic field produced by the applied alternating current causes an opposing current, and voltage in the rings and collars. The generation of an opposing current is an illustration of Lenz's law.
This induced current gives rise to a magnetic field oriented to repel against the field that forms in the ring launcher coils. The repulsion between these magnetic fields causes the ring to be tossed.
Because copper is a better conductor than aluminum or lead, more current flows and the ring is tossed higher. The collars are heavier and are not thrown as far. The split rings do not provide a complete current path, so the induced current does not flow in a complete circuit. The bulb lights because a current is induced in the coil connected to the bulb. The liquid nitrogen reduces the resistance of the rings. With lower resistance, more current can flow. The higher current creates a stronger magnetic field, which launches the ring higher.
Other Things to Try
The current generated in the split ring can be measured by attaching an AC voltmeter or a multimeter configured as an AC voltmeter.
The Point
A current flowing in a conductor produces a magnetic field. A changing magnetic field can induce a current in a conductor. The induced current can then generate a current. These currents according to Lenz's law will always oppose each other.
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