What a learner can do afterwards
- Predicts the direction of an induced current and names the change it opposes
- Argues that the opposite sign would let a machine make energy from nothing
- Relates the peak emf and the frequency of a generator output to how the coil is turning
1 · Read
Lenz fixes the direction: the induced current flows so its own field fights the change that made it. Push a north pole in and the near face turns north to repel it. Pull out and it flips south to hold back. No change means no current at all.
The minus sign in Faraday's law is this fight in symbols. Flip the sign and a magnet would be sucked in and spat out while lighting bulbs: free energy from nothing. Since that cannot happen, Lenz is an energy argument, not just a rule.
A coil turning steadily in a field gives output that swings as a sine curve. Spin rate sets the frequency, and turns, area, field, and spin rate together set the peak emf. Double the spin and both the frequency and the peak double.
Fight the change for direction, bill it to energy, and spin faster for taller faster output.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.