magnetic field
induced current
induced voltage (EMF)
Drag the magnet ↔ through the coil
Flux through coil
0.00 mWb
Grab the magnet and move it through the coil. Watch the needle and the traces below.
EMF = − N · dΦ/dt = 0.00 V
N = 50 turns ·
rate of flux change dΦ/dt = 0.000 Wb/s.
The minus sign is Lenz's law: the induced current opposes the change that made it — the coil pushes back.
Notice EMF depends on how fast the flux changes, not on how much flux there is.
Teaching notes
- The one move to make live: drag the magnet to the center of the coil and hold it still. Flux is at its maximum, yet EMF and current fall to zero. It's the change in flux that matters, not the amount.
- Then turn on Auto-oscillate — a magnet swung back and forth produces alternating voltage. This is the seed of every AC generator (Module 2).
- Use the sliders to show the three levers of Faraday's law: more turns, a stronger magnet, or faster motion all raise the induced voltage.
- Flip to Equation view for a technical audience: EMF = −N·dΦ/dt updates live with the values on screen.
Flux Φ(t), mWb — depends on where the magnet is
EMF(t), volts — depends on how fast flux changes
EMF peaks where the flux curve is steepest; it's zero where flux is flat, and flips sign when the magnet reverses (toward vs. away) or you flip the poles.