Faraday's Law Lab — Magnet, Coil and Galvanometer
A bar magnet, a coil of copper wire and a centre-zero galvanometer on one bench: Faraday's experiment in three steps. Push the magnet in and the needle kicks; hold it still inside the coil and the needle falls back to zero, even though the flux is now at its largest; pull it out and the needle kicks the other way. Four one-click comparisons then measure what sets the size of the kick.
How to use this simulation
- Run the experiment: the one primary button plays the three steps in order — push in, hold still, pull out.
- Each step button runs that step on its own, and the panel beside the scene says what is happening now and what to watch next.
- Compare two pushes: four buttons each run a measured pair of trials — twice as fast, twice the turns, the magnet flipped, and the coil moved instead of the magnet.
- Drag the magnet or the coil along the axis yourself, and click the knife switch on the bench to open or close the circuit.
- Adjust the apparatus holds the push speed, a continuous in-and-out or right-through motion, the number of turns, the magnet's strength, the circuit resistance and the meter range; More measurements adds live graphs of Φ and ε and a data export.
What to look for
- The needle moves only while something moves: at rest inside the coil the flux is largest and the current is zero.
- Pushing in and pulling out swing the needle in opposite directions.
- The end of the coil facing the magnet becomes the same pole as an approaching magnet pole and the opposite pole as it leaves — the push-back of Lenz's law.
- Twice the speed or twice the turns gives twice the peak current; flipping the magnet gives the same size of kick the other way.
- With the switch open an emf is still induced, but no current flows.
The physics behind it
Faraday's law says the emf induced in a coil equals the rate of change of the flux linking it, ε = −N ΔΦ/Δt. The lab works out the flux through every turn separately, from a magnet modelled as a line of tiny dipoles, adds the turns into the flux linkage NΦ and differentiates, so every reading is calculated rather than animated. A magnet at rest gives the largest flux and no emf at all. Doubling the speed of the same push doubles the rate of change and so the peak current; doubling the turns doubles the emf. Lenz's law fixes the direction: the induced current always opposes the change, so an approaching N pole meets an N pole on the coil and is repelled, while a retreating one is pulled back by an S pole. Only relative motion matters: sliding the coil onto a fixed magnet gives exactly the same kick.