# The Use of Superconductors & Magnetic Levitation in Transportation

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What is a superconductor? The potential for magnetic levitation in transport is huge and exciting. Learn what superconductors are and how they are used to levitate objects, then take a quiz to see how much you've retained.

## What Is Superconductor Levitation?

Superconductors are special materials that have exactly zero electrical resistance when cooled below a particular temperature, which we call the critical temperature. Resistance is a property that holds back flow of electricity. So an object with zero resistance would conduct electricity perfectly.

Conductivity is the opposite of resistance: it's the tendency for electricity to flow. A high resistance material has poor conductivity, and a low resistance material has high conductivity. A conductor is any material that conducts electricity at all. So superconductors are materials that are super at conducting (at least at the right temperature).

Superconductivity was discovered in 1911. It is explained by quantum mechanics and is a state where the inside of the conductor contains no magnetic field lines. With most superconductors, it's a sudden change that occurs exactly when you hit a particular temperature in the process of cooling a metal. These are called type I superconductors. Type II superconductors are ones where it isn't such a sudden change.

Superconductors are considered to be perfect diamagnets. A diamagnet is a material that shows repulsive magnetic effects when it is put inside a magnetic field. Or in other words, if you put a diamagnet near a regular magnet, it will be pushed away (or repulsed) from it. All materials are at least somewhat diamagnetic. For this reason it is possible to float a small animal like a frog inside a magnetic field. This is called diamagnetic levitation. But superconductors are even more diamagnetic, so you can use them to levitate things more easily.

## Applications of Levitation in Transport

Superconductors themselves have many applications, and those applications are largely in the form of magnetism. By having a material that conducts perfectly, you can build some incredibly powerful electromagnets. An electromagnet is a magnet that is created by running an electric current through a coil of wire. The magnetic field it creates is similar to that of a bar magnet. These electromagnets are used in particle accelerators to discover more about the universe, but they can also be used in magnetic resonance imaging (MRI) machines in hospitals to take pictures of the inside of the human body. They're also used to create radio frequency (RF) and microwave filters in cell phone technology. In the future they could be used to build smart grids, store electricity, and create more efficient refrigeration.

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