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Pedal a bike on a stand. How does turning a magnet light the lamp?
Bike Dynamo lab · Last updated: 16 October 2026
A bicycle stands on a rack with a dynamo pressed against its wheel. You pedal, and the lamp lights up. Pedal faster and it glows brighter. Inside the dynamo, a spinning magnet is doing something remarkable.
What you'll discover
- Moving a magnet near a coil of wire makes an electric current flow.
- Spinning the magnet faster makes a bigger voltage, so the lamp shines brighter.
- Your pedalling energy is turned into electrical energy, then into light.
The science in plain words
Inside a bicycle dynamo is a small magnet that spins when the wheel turns it. Around the magnet are coils of copper wire. As the magnet turns, the magnetic field passing through the coils keeps changing, and a changing magnetic field pushes electrons along the wire. That push is a voltage, and it drives a current through the lamp.
This effect is called electromagnetic induction, discovered by Michael Faraday in 1831. The faster the field changes, the bigger the voltage. So pedalling faster spins the magnet faster and makes the lamp brighter. Stop pedalling and the lamp goes out, because a still magnet makes no current.
Because the magnet's north and south poles take turns passing the coil, the current flows one way, then the other: it is alternating current.
A dynamo is a small generator, and almost all the world's electricity is made the same way. In power stations, steam, water or wind turns huge magnets inside coils. Energy is never created from nothing: the rider feels the pedalling get slightly harder when the lamp is connected, because their energy is being turned into electrical energy.
Where it fits
- India, NCERT: Electromagnetic induction is taught in NCERT Class 12; this lab builds on Class 10 Chapter 12: Magnetic Effects of Electric Current.
- United States: Grades 9 to 12
- Next Generation Science Standards: HS-PS2-5
Common questions
How does a bicycle dynamo work?
The turning wheel spins a magnet inside a coil of wire. The changing magnetic field pushes electrons around the circuit, making a current that lights the lamp.
Why is the bike light brighter when you pedal faster?
A faster-spinning magnet changes the magnetic field through the coil more quickly, which makes a bigger voltage and a bigger current, so the lamp shines more brightly.
What is the difference between a motor and a generator?
They are built in a similar way but work in opposite directions. A motor uses electricity to make movement; a generator uses movement to make electricity.
Related labs
- Magnet Drop: Drop a magnet through a coil of wire. Can a falling magnet make electricity?
- Power to the Town: Change the turns on a transformer. Can you make the street lamps brighter, or blow them?
- Magnet and Compasses: Slide a magnet and compasses round a desk. Which way do the needles point, and why does a far one wobble slowly?
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Try it yourself
The Bike Dynamo lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.