# The Role of Magnetic Force in Technological Devices

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.

After completing this lesson, you will be able to explain what magnetic forces are, and describe various technological devices that use magnets. A short quiz will follow.

## What is Magnetic Force?

A magnetic force is a force felt from a nearby magnet, or electric current (a moving charge). An example of an electric current would be electricity moving through a wire. Both magnets and electric currents produce magnetic fields. A magnetic field is the area where other magnetic materials will feel a force. The magnetic field is stronger the closer you are to a magnet or electrical wire.

But don't electric charges in a wire produce electric, not magnetic, fields? After all, that's where the word electricity comes from. Well, it turns out that only stationary charges produce electric fields. Moving charges produce magnetic fields.

What is it about magnets that makes them create a magnetic field? The truth is that magnetic materials are only magnetic because of electric currents inside them. For example, a big lump of iron -- the same material many bar or horseshoe magnets are made of -- has charges moving inside of it. It's the way those charges move that give iron its magnetic properties.

Magnets have north poles and south poles: opposite poles attract, and like poles repel. We can use this to our advantage. We can use magnetism to apply force to objects: to attract and repel them. Today we're going to talk about how magnetic forces are used in modern technology.

## Technological Applications of Magnetic Forces

There are many real-life uses of magnets, some of which might seem pretty minor, while others are a really big deal.

One of the bigger and more impressive uses is in MRI scanners. An MRI machine is essentially a gigantic magnet that aligns the magnetic dipoles in your body. Magnetic dipoles are particles in your body that act like tiny magnets. By seeing how fast the dipoles in your body line up, pictures can be created of the inside of your body. This is possible because certain tissues have dipoles that align quicker than others. This technology allows doctors to diagnose all kinds of diseases.

A smaller, but still interesting use is in a traditional alarm or school bell. The bell contains a hammer which can drop to hit the bell. But when it drops, it connects a circuit, powering an electromagnet, which lifts the hammer back up again. Lifting up breaks the circuit, and the hammer falls all over again. In this way the cycle repeats and the bell is hit over and over. This was how school bells rang out for decades before electronics became more advanced.

Power plants are another huge application. Electric power generators also use magnetism. It turns out that when you move an object through a magnetic field, electricity is created. Power plants create steam, and that steam turns a turbine between the poles of a large magnet, creating electricity. This is how all power plants work. So even electrical devices that contain no magnets at all, wouldn't exist without magnetism!

Maglev trains are an exciting new application of magnetic forces. Using powerful electromagnets, these kinds of trains, found in Germany and Japan, levitate above the tracks. (Remember: like poles repel!) Why is that helpful? Well, by levitating, they avoid friction entirely. This allows the trains to save energy, and reach incredibly fast maximum speeds. How fast? In early 2015, a Japanese train of this kind reached 374 miles per hour.

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