What a learner can do afterwards
- Describe that a current is produced when a wire or coil moves through a magnetic field, or the field around it changes
- Predict how to induce a bigger current (move faster, add turns to the coil, use a stronger magnet) and what happens when the motion stops
- Explain why a generator produces alternating current, linking it to a real example such as a bike dynamo or a power-station turbine
The lesson
Move a wire, or a coil of wire, through a magnetic field, and something happens: a current appears in it, with no battery in sight. It also works if the coil stays still and the field around it changes instead. Michael Faraday discovered this in the 1830s, and it is called electromagnetic induction. You already know the motor effect, where current through a wire in a field creates movement. Induction is the reverse: movement through a field creates a current.
A bike dynamo is a small generator that presses against the spinning wheel. As the wheel turns, it spins a magnet past a coil inside the dynamo, and that motion induces a current that lights the lamp. Pedal harder, and the light gets brighter. Stop pedaling, and the light goes out straight away, because the current only flows while the magnet is moving.
Power stations work the same way, just bigger: steam or falling water spins a giant coil inside a strong magnet, generating electricity for entire towns. Every half turn, the coil moves through the field in the opposite direction, so the current keeps switching too. That is why generators make alternating current instead of the one-way direct current a battery gives.
Moving a coil through a magnetic field induces a current, faster motion, more turns, or a stronger magnet make it bigger, and a spinning coil turns that current into alternating current.
Watch it
Where it sits
This opens up
Nothing builds on it yet.
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.