The live graphs plot the EMF and the flux linkage, and the coil's induced north and south poles light up so you can see Lenz's law at work. The numbers use real units: a 100-turn coil and a strong magnet give millivolts.
- What is electromagnetic induction?
- Electromagnetic induction is the making of an EMF (a voltage) in a coil by changing the magnetic flux through it. Move a magnet in or out of a coil, or spin it, and a current flows with no battery. Michael Faraday discovered it in 1831.
- What is Faraday's law?
- Faraday's law says the induced EMF equals the number of turns times the rate of change of magnetic flux: ε = −N dΦ/dt. More turns, a stronger magnet or faster motion all give a bigger EMF. If the flux is not changing, the EMF is zero.
- What is Lenz's law?
- Lenz's law says the induced current flows in the direction that opposes the change in flux that caused it. That is the minus sign in Faraday's law. Push a north pole at a coil and the coil end facing it becomes a north pole and pushes back.
- Why is there no EMF when the magnet is still?
- An EMF needs a changing flux. A magnet held still inside the coil gives a steady flux, so dΦ/dt is zero and so is the EMF, however strong the magnet is.
- How does an AC generator work?
- A magnet (or coil) is spun so the flux through the coil is Φ cos θ. Its rate of change is a sine wave, so the EMF alternates. Power stations do this with turbines.
- How do I get a bigger EMF?
- Move the magnet faster, use more turns, use a stronger magnet or spin the generator faster. The EMF is proportional to each of these.