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Switch on the crane magnet. How many cans can it grab, and how do you make it stronger?
Scrapyard Crane lab · Last updated: 16 October 2026
You switch on a scrapyard crane magnet, count how many cans it can lift and then work out how to make it stronger. Electromagnets are magnets you can turn on and off, and they sit inside door locks, speakers, motors and the cranes that sort scrap metal.
What you'll discover
- An electric current flowing through a coil of wire makes a magnetic field, and switching it off makes the magnet let go.
- More current or more turns of wire make the electromagnet stronger.
- An iron core inside the coil makes the magnet far stronger than the coil on its own.
The science in plain words
Whenever electric current flows through a wire, it makes a magnetic field around the wire. A single wire gives a weak field, but wind the wire into a coil and the fields from every turn add together. The coil then behaves like a bar magnet with a north and a south pole. This kind of coil is called a solenoid.
Put a piece of soft iron inside the coil and the field becomes much stronger. Iron is made of tiny regions called domains, each a small magnet. The coil's field lines these domains up, so the iron itself becomes a strong magnet for as long as the current flows. Switch the current off and soft iron loses most of its magnetism, which is why the crane drops its load.
There are three main ways to make an electromagnet stronger: increase the current, add more turns of wire, and use an iron core. Reversing the direction of the current swaps the north and south poles. Scrapyard cranes use this switchable strength to lift iron and steel, while aluminium cans, which are not magnetic, stay behind. The same idea is used in electric bells, relays, loudspeakers, MRI scanners and the motors in fans and cars.
Where it fits
Common questions
How do you make an electromagnet stronger?
Increase the current flowing through the coil, wind more turns of wire around it, or put a soft iron core inside it. Each of these strengthens the magnetic field. Using all three together makes the biggest difference, which is how industrial lifting magnets are built.
What is the difference between an electromagnet and a permanent magnet?
A permanent magnet is magnetic all the time. An electromagnet is only magnetic while current flows through its coil, so it can be switched on and off, and its strength can be changed by changing the current. That control makes electromagnets useful in machines.
Why can a scrapyard magnet not pick up aluminium cans?
Aluminium is not attracted to magnets in the way iron, nickel and cobalt are. A crane magnet can lift steel cans because steel is mostly iron, but aluminium drink cans stay on the ground. Recycling plants use this difference to sort metals.
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- Bike Dynamo: Pedal a bike on a stand. How does turning a magnet light the lamp?
- Simple Circuits: Close the switch. What makes the bulbs brighter: more volts, fewer bulbs, or a different wiring?
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Try it yourself
The Scrapyard Crane lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.