Needle Moving Without a Battery? A Magical Coil-and-Magnet Experiment (Electromagnetic Induction)

Ken Kuwako, Science Trainer here. Every day is an experiment.

No batteries. No outlet. Just a magnet moving near a coil, and suddenly electricity flows. No matter how many times I see it, it still makes me say, “Wait, what?!” This is electromagnetic induction. Move a magnet toward a coil and current flows. Hold it still and the current stops. Pull it away and the current flows again. The energy from your moving hand (kinetic energy) turns into electrical energy, which is pretty amazing when you think about it. In this article, I’ll show you how to experience electromagnetic induction for yourself.

First, a Teacher Demonstration

We started with a demonstration by the teacher, using Pascal wire. The wire was connected to a galvanometer (a device that detects very small electric currents), and then a magnet was moved toward and away from the wire.

Next, the Pascal wire was wound into a coil, and the same experiment was repeated. Keep an eye on the galvanometer needle. How does its movement differ between a single straight wire and a coil?

Now It’s the Students’ Turn!

Next, the students got to try the experiment with their own hands.

What You’ll Need

・Pascal wire
・A coil
・A bar magnet
・A galvanometer

Steps

1　Move the magnet toward and away from the coil, and watch how the galvanometer needle moves.

2　Change how you move the magnet (try moving it quickly, then slowly).

3　Swap in a coil with a different number of turns and repeat the experiment.

4　Stack two magnets together and try it again.

What to Look For

As you experiment, keep these points in mind.

What happens to the needle when you bring the magnet closer versus when you pull it away? In general, the needle swings in opposite directions. And when you stop moving the magnet, the needle returns to zero. Current flows only while the magnetic field (the space where a magnet’s force acts) inside the coil is changing.

Move the magnet quickly, and the needle swings wider. That’s because the faster the magnetic field changes, the stronger the current (called induced current) becomes. Adding more turns to the coil, or stacking two magnets to make a stronger magnetic field, will also make the needle swing wider. Try making a prediction before you test it. The results are way more fun that way!

Electromagnetic Induction Is All Around You

This principle quietly powers our everyday lives. Generators in power plants make electricity from the relative motion of magnets and coils. It’s also at work in bicycle dynamos, in the IC cards you tap to pay for things, and in wireless phone chargers. A small experiment in the science room connects to some of the biggest systems in our society.

Contact and Requests

Let’s bring the wonder and fun of science closer to everyday life! This site collects science experiments you can enjoy at home, along with tips for making them work. Go ahead and search around!
・The contents of Kagaku no Netacho (Science Idea Notebook) have been published as a book. Details are here
・Learn more about the site’s author, Ken Kuwako, here
・For requests of all kinds (writing, lectures, science workshops, TV supervision and appearances, and more), please click here
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