Electromagnetic induction

Here is a battery, a lamp, and a conductor. And next to the conductor there is a magnet which can rotate: a compass. When an electric current runs through the conductor the compass turns, because the current creates a magnetic field around the conductor. If we turn the battery the other way around, and let the current run in the other direction, the magnetic field is also turned around. And the compass turns the other way.

So, electric current causes a magnetic field. Does it work the other way around too? Can a magnetic field cause electric current? Let’s connect the conductor to a galvanometer. The meter shows zero.

There is no current running through the conductor. Let’s place a magnet close to it, and yes, now there is current running through the conductor. But now the meter shows zero again, even though the magnet is right next to the conductor. Let’s remove the magnet, and hang on! There was current running in the conductor when we were removing the magnet too.

And if we bring the magnet back, there is current for a brief period again. But when the magnet is still, the current in the conductor stops. It’s when the magnet moves, that the current appears. Changes in the magnetic field induce a current in the conductor. This is called induction, and the current is an induction current.

The magnetic field only affects a small part of the conductor. But if we bend the wire into a loop, a larger section of the conductor can be affected by the magnetic field. The induction current becomes stronger. And the more times we wind the wire, the stronger the current gets. A conductor wound into loops is called a coil.

So, if the magnet is in motion an induction current occurs in the conductor. Now, Kim is spinning a magnet which they are keeping close to a conductor, wound into a coil. The magnet is in motion, and the magnetic field is constantly changing. A current is induced in the conductor. The current makes the light shine.

Now Kim can have a rest. Let’s replace them with a waterfall! Now, the running water is what makes the magnet spin. And the light keeps shining. A magnet that rotates close to a coil causes a current.

The magnet generates current in the coil. This is a simple generator. A generator transforms kinetic energy into electrical energy. If the magnet spins faster, the current becomes stronger, and the light shines more brightly. Let’s exchange the light for a galvanometer again.

When the magnet turns, the current first runs in one direction and then in the other direction. The current alternates its direction all the time. A generator produces alternating current. Compare it to the battery. Here, the current always runs in the same direction.

This is direct current. Changes in a magnetic field induce current in a conductor, an induction current. Induction can be used to transform kinetic energy into electrical energy, in a generator.