Unit 11, lesson 54. About 12 minutes.

Electromagnets and motors

How can electricity spin the wheels of a train?

Play

Getting the experiment ready…

Explain

Electricity can make a magnet.

Magnets can spin a motor.

When electricity flows in a wire, it makes a magnetic field around it. Wrap the wire into a coil, and the field gets stronger.

That is an electromagnet. It can be turned on and off, and more turns or more current make it stronger.

A motor uses magnetic forces on a coil to turn electricity into spinning.

Field strength rises with the current and with the number of turns. An iron core makes it much stronger.

In a motor, a current-carrying coil sits in a field, and feels forces that turn it.

A generator does the reverse: spinning a coil in a field makes electricity.

Current makes a field
A coil makes it strong
Forces spin a motor

Want the full story?

The number of paper clips in the sim is only illustrative. Michael Faraday showed that electricity and magnetism are closely linked, and James Clerk Maxwell later united them in one theory. Power stations make electricity with generators.

The Formula

strength goes up with turns of wire × current

B \propto n \times I

$B$: the strength of the magnetic field, measured in teslas (T)
$n$: the number of turns of wire, which has no unit
$I$: the current, measured in amps (A)

Try the numbers

Turns of wire: 20Current: 2 A

Turns × current: 40 amp-turns

Try it at home

You need a notebook, a pencil.

You need: a notebook, a pencil.

Find things at home that spin.

Look around your home for things that spin.
Fans, washing machines and toy cars all use motors.
Make a list of them.

What's happening: nearly everything that spins using electricity has an electric motor inside.

Physics is life

Your body

Your muscles work like tiny motors.

Tiny molecular motors in your muscles use energy to pull and move you.

Daily life

Scrapyards lift cars with magnets.

Electromagnets lift scrap cars, and they can be switched off to drop them.

Nature

Wind turbines make electricity.

Wind spins generators, and that makes electricity with no fuel at all.

Space

Rovers use electric motors.

Rovers on Mars drive with electric motors, powered by the Sun or a small nuclear battery.

Quick check

Question 1 of 3

How can you make an electromagnet stronger?

Words to know

Electromagnet: A magnet made by electricity flowing through a coil.

Electromagnet: A magnet made by electricity flowing through a coil.
Motor: A machine that turns electricity into movement.
Current: The flow of electric charge. It is measured in amps.

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Electricity in your body