Magnet Dropped in a Ring or a Coil
Drop a magnet through a coil and the EMF trace is not one clean pulse but two, of opposite sign and different shapes. This 3D simulation graphs the induced EMF in real time as the magnet accelerates under gravity, making the asymmetry easy to explain.
How to use this simulation
- Choose a single ring or a multi-turn coil
- Set the drop height and the magnet's strength
- Reverse the magnet's polarity
What to look for
- Two EMF pulses of opposite sign, one as the magnet enters and one as it leaves
- The exit pulse is sharper and taller because the magnet is moving faster
- Flipping the magnet flips both pulses, confirming the sign comes from Lenz's law
The physics behind it
Faraday's law gives ε = −N·dΦ/dt. As the magnet approaches, flux through the coil grows and one polarity of EMF appears; as it leaves, flux falls and the EMF reverses. Because gravity has accelerated the magnet by then, the exit happens faster, so the second pulse is taller and narrower than the first while enclosing the same area.