EASA Part-66 · Module 3 — 3.10 Inductance / Faraday · B1/B2

Electromagnetic Induction — Faraday & Lenz

Objective: show that a changing magnetic flux induces an EMF (e = -N dΦ/dt) and that the induced current opposes the change that caused it (Lenz's law).

Magnet moving through a coil

Induced EMF vs time

Magnet speed 1 ×

Magnet strength 0.8

Coil turns N 80

Flux Φ (rel.)

Rate dΦ/dt

EMF

0mV

Direction

e = −N·dΦ/dt (Faraday) · sign opposes the change (Lenz)

An EMF appears only while the flux through the coil is changing. The faster the magnet moves, the stronger the magnet, and the more turns, the bigger the EMF. The induced current always flows so as to oppose the change that produced it (Lenz's law) — so the polarity flips between the magnet approaching and leaving.

Try this: Hold everything else and increase the magnet speed. Watch the EMF peak grow.
Try this: Note the EMF when the magnet sits still at the centre. Why is it zero there?
Try this: Double the turns N. The EMF should roughly double for the same motion — why?