Physics

Electromagnetic induction

Faraday's law live: a magnet falling through a coil induces a current, Lenz brakes the fall for real - plus the copper pipe, a transformer and a generator.

By Mykhailo Makarov

Actual application image

What happens

Drop the magnet through the coil and watch the flux, the EMF and the current draw themselves - with the circuit closed the magnet lands measurably later, and the energy books balance: what the fall loses, the resistor turns into heat. Grab the magnet with the mouse and wave it yourself, or try the copper pipe, where eddy currents float the magnet down at a crawl. Then switch the magnet for an electromagnet, couple two coils into a transformer, and crank the generator - the harder the lamp loads it, the harder it is to turn.

Equations used in the module

Equations
ε = −N dΦ/dt   (Faraday)
Lenz: the current opposes the change
brake: F = −(B² l² v) / R  →  terminal speed in the pipe

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