Electromagnetic induction – magnet and coil, alternating current
Integrated ScienceElectricity & MagnetismAges 14–15
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Electricity & Magnetism
Move a bar magnet in and out of a coil (by hand or automatically); the galvanometer needle deflects according to the speed and the number of turns, and returns to zero when the magnet stops. Switch to the rotating-magnet mode to see the induced EMF reverse direction periodically – alternating current. An EMF-vs-time graph, the number of field lines through the coil, and the direction of the induced current all update continuously.
Lesson: Electromagnetic induction, alternating current
What it shows
Electromagnetic induction produces an EMF in a coil whenever the magnetic flux through it changes. By Faraday's law, e = −ΔΦ/Δt with Φ = NBS, so a faster magnet or a coil with more turns gives a larger EMF, while a magnet resting inside the coil gives none, however strong its field. The minus sign (Lenz's law) means that pushing the magnet in and pulling it out drive current in opposite directions. When the magnet rotates, the flux rises and falls periodically, so the EMF reverses every half turn: the principle of an AC generator.
How to use
Choose Drag by hand and move the magnet slowly, then quickly, into and out of the coil while students watch the galvanometer needle; hold the magnet still inside to show the needle return to zero. Switch to Auto in/out and compare several values of N and magnet speed on the e(t) graph. Finally press Rotating magnet and relate the shape of the graph to alternating current.
Parameters you can change
- Number of turns N 5–200 turns
- Magnet speed (auto/rotate mode) 5–60 cm/s
- Pole entering the coil first North pole (N), South pole (S)
- Mode Move magnet by hand, Magnet moves in and out automatically, Rotating magnet (alternating current)
- Show magnetic field lines
Questions to explore
- Why is there no induced current when the magnet rests inside the coil?
- What are two ways to make the galvanometer needle deflect further?
- When the magnet rotates, why does the induced current keep reversing direction?
