Ages 8–12 · about 7 minutes
The Metal That Lets Electricity Run Free
What is a superconductor, and what is it good for?
The big idea
A superconductor does not make energy. It stops wasting it — electricity runs through it with nothing in the way at all.
Do this first · Try this at home
The ball that keeps going, and the ball that gives up
Start with your hands. The reading makes far more sense afterwards.
You need: A ball that rolls, a smooth hard floor, a bath towel, two socks to use as markers, and an adult with you
0 of 3 steps done
What should I notice?
Notice: The same push carried the ball much further on the floor than on the towel. Nothing took the push away — something along the way ate it. The towel eats a lot, the floor eats a little, and a superconductor eats none. That is the whole idea: not a smoother floor, but a floor that takes nothing at all.
Now read on to find out why it happens.
- resistance
- The way most materials fight electricity a little, and turn some of it into heat.
- superconductor
- A material that, when it is cold enough, lets electricity flow with no resistance at all. Only some materials do this, and only when they are very cold.
- levitate
- To hang in the air with nothing holding you up from below.
What is a superconductor, and what is it good for?
Push electricity through an ordinary wire and the wire fights back a bit. Some of the power turns into heat. It does not do the job you wanted. That fight is called resistance. It is why a charger gets warm in your hand.
A superconductor does not fight back at all. Not a little. None.
Cool the right material far enough and something switches. Electricity then runs through it with nothing in the way. Send a current round a loop of it. The current keeps going round by itself, with nobody pushing it.
It pushes magnets away
Bring a magnet near a cold superconductor and the superconductor pushes back.
It makes magnetism of its own, aimed the other way. So the magnet's field cannot get inside. Let go, and the magnet hangs in the air above it. You can see straight through the gap. That is the photograph in the picture up there. The US Department of Energy explains what goes on inside: DOE explains superconductivity.
Gravity has not been switched off under that floating magnet. Earth pulls it down as hard as ever. The push from the superconductor holds it up by the same amount.
The cold is the hard part
Every superconductor we have has its own temperature. It only does the trick below that. All of those temperatures are far colder than a kitchen freezer. So the cooling is done with liquids colder than anything you should ever touch.
That is why this is a job for a laboratory, with trained people. It is not a thing to try on your table at home. Your ball and your towel are the part you can do.
One more thing, and it matters. A superconductor does not make energy. It is not a battery. It is not a magic engine. It carries what you give it and wastes none of it on the way. Wasting nothing is already a big deal.
What people build with them
Hospital scanners. The big machine that takes a picture of your insides, without cutting you open, is built around a huge magnet. That magnet is a coil of superconducting wire. An ordinary coil that strong would cook itself.
Floating trains. Some trains ride above their track instead of on it. Magnets hold them up and push them along. No wheels touching means no rattling and no rubbing.
The best magnet detectors there are. Superconducting loops can notice magnetic fields far too faint for anything else. Even the tiny magnetic whisper of a beating heart.
What a warm one would change
Scientists are hunting for a material that does this without the cold. People call it a room-temperature superconductor.
It would not be a new kind of magic. It would be the same trick, with the hard part taken out. No very cold liquid. No heavy cooling gear. No bill for keeping it cold. Scanners could be smaller. Wires could carry power across a country and lose none of it.
So people keep looking, and they look carefully. Careful matters here. A material that does it has to do it again, in somebody else's laboratory, on somebody else's day.
Your turn
Find three things at home that get warm while they work. A charger, a lamp, a laptop. That warmth is the electricity paying a toll on the way through.
Then ask the good question. If you could take the toll away, what would you build first?
For grown-ups and older readers
This lesson comes from Chapter 11: Gravity Control and Superconductors and the map unit Gravity control and superconductors.