Making Electricity With a Moving Magnet
- Physics
- Ages 14–18 · Grades 9–12
- Hands-on experiment
What you’ll find out
- A changing magnetic field through a coil induces a voltage across it.
- Faster movement, more turns and a stronger magnet all increase the induced voltage.
- The induced current opposes the change that produced it, so generating takes work.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Faraday’s discovery
An electric current makes a magnetic field. Michael Faraday asked the opposite question: can a magnetic field make a current? In 1831 he wound a coil of wire, joined it to a meter, and pushed a magnet into the coil. The needle flicked. He held the magnet still inside the coil, and the needle fell back to zero. He pulled the magnet out, and the needle flicked the other way. Movement, not the magnet itself, is what matters. Only a changing magnetic field through the coil produces a voltage, and that is called electromagnetic induction.
Why generating takes effort
Push a magnet into a coil and you can feel it resist. That is not friction; it is a law. The induced current makes its own magnetic field, and that field always opposes the change that created it, which is known as Lenz’s law. So you have to do work to keep the magnet moving, and the work you do becomes the electrical energy delivered by the coil. Power stations run on this idea. Steam, falling water or wind turns a turbine, the turbine spins a magnet near coils of wire, and the electricity flows out. When more people switch appliances on, the turbine becomes harder to turn.
Curriculum links: NGSS HS-PS2-5 · NGSS HS-PS3-3