Lenz's Law (Magnetic Braking)
Drop a bar magnet through a conducting coil — watch the induced current reverse direction between approach and withdrawal, and see the braking force it creates slow the fall, exactly the classic 'magnet through a copper tube' demonstration.
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What you can adjust
- Coil turns (N)
- 10 – 300 turns
- Magnet strength (Φ0)
- 0.001 – 0.015 Wb
- Coil resistance (R)
- 1 – 100 ohm
- Magnet mass
- 0.03 – 0.3 kg
More turns mean a bigger induced EMF for the same changing flux — and a stronger braking force.
The peak magnetic flux the magnet threads through the coil at closest approach — a stronger magnet means stronger braking.
Must be above 0. Lower resistance lets a bigger induced current flow for the same EMF — like a real conducting tube — braking the fall much harder.
A heavier magnet carries more momentum into the coil, so the same braking force slows it relatively less.
About this simulation
What it shows
A bar magnet is dropped through a coil. A current appears in the coil, its direction reverses between approach and exit, and the magnet falls more slowly than it would freely.
The key idea
The induced current always opposes the change that causes it (Lenz's law), so it pushes back on the falling magnet. A stronger magnet, more turns or a lower coil resistance give a bigger current and a stronger braking force.
Try this
Lower Coil resistance (R) from 3 to 1 ohm: more current flows, so the braking is stronger and the magnet falls more slowly.
The flux through the coil is modelled with the same smooth bell-shaped curve as the induction simulation, which is a simplification of a real magnet and coil.