Electromagnetic Induction – Magnet, Coil and Galvanometer
PhysicsElectric & Magnetic FieldsAges 17–18
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Electric & Magnetic Fields
Drag a bar magnet into or out of an N-turn coil connected to a galvanometer, or let the magnet move by itself. The needle deflects in proportion to the rate of change of magnetic flux and reverses when the direction of motion or the pole is reversed; when the magnet is at rest the needle returns to zero. Graphs of the flux Φ(t) and the induced EMF e = −N·ΔΦ/Δt run continuously, and the direction of the induced current given by Lenz's law is shown on the coil.
Lesson: Electromagnetic induction, Faraday's law and Lenz's law
What it shows
Electromagnetic induction happens whenever the magnetic flux through a coil changes. Here a bar magnet moves along the axis of a coil wired to a centre-zero galvanometer. The flux Φ through the N turns depends on how far the magnet is inside the coil, and Faraday's law gives the induced EMF as e = −ΔΦ/Δt, so the needle responds to how fast the flux changes, not to how large it is. Lenz's law sets the direction: the induced current makes the nearer end of the coil a pole that repels an approaching magnet and attracts a receding one.
How to use
Start with Auto in/out to see a steady pattern, then drag the magnet by hand: push it in quickly, then slowly, and hold it still inside the coil while watching the galvanometer and the EMF graph. Use Flip magnet to turn the other pole towards the coil and compare the needle direction. Finally raise Number of turns N or the magnet strength and repeat the same motion to see which factors increase the induced EMF.
Parameters you can change
- Number of turns N 50–1000 turns
- Magnet strength (remanent flux density) 0.1–1.2 T
- Magnet speed in auto mode 5–60 cm/s
- Pole facing the coil North pole (N), South pole (S)
- Magnet moves in and out automatically
Questions to explore
- Why does the galvanometer read zero while the magnet rests inside the coil, even though the magnetic field there is strong?
- When the north pole approaches the coil, which pole forms at the nearer end of the coil, and how does this agree with Lenz's law?
- What three changes increase the induced EMF, and how does the EMF graph confirm each one?
