Major Funding The Laura Moore Cunningham Foundation



Magnets: Facts

You have probably played with magnets before, and it is likely that you have a magnet or two on your refrigerator, holding up a note or a picture. You may have seen magnets shaped like horseshoes, rectangular bars, or round discs. Magnets are fun to play with and useful for sticking things together. But did you know that magnets are everywhere, doing important work that we benefit from every day? Did you know the power of magnetism even allows life to exist on Earth? How do magnets work? Let's find out more.

What Are Magnets?

A magnet is an object that can pull certain types of metal toward itself (attract), or push those metals away (repel). Magnetism refers to the invisible force of magnets and is a property of certain substances. Magnetism is a basic force of nature, like gravity or electricity. Even though we can't actually see magnetic force, we can see what the force does to things around it. Magnetism can work over a distance, meaning that a magnet does not have to be touching an object to attract it or repel it.

Not all metals can be magnets. Only certain metals have magnetic properties, namely iron, nickel, cobalt, and a few rare-earth metals such as neodymium. Today, magnets are usually made of alloys containing these metals. Many metals, such as aluminum and copper, are not attracted to magnets. That's why a magnet can pick up an iron nail or a steel paper clip, but not an aluminum soda can or a copper penny. Other materials such as plastic, wood, and paper are not attracted to magnets.

People have known about magnets for thousands of years. According to legend, one day a Greek shepherd found that the nails in his shoes stuck to a rock he was standing on. That rock was lodestone, containing the mineral magnetite. The Chinese knew how to use lodestone to make compasses 2,000 years ago. To ancient people, magnetism seemed like magic. It is only in the last century that science has understood why magnets work.

courtesy explainthatstuff.com

All matter of made of atoms. Atoms contain electrons, which are tiny charged particles that, in most substances, spin in different random directions. However, in magnetic materials such as iron, the electrons spin in the same direction. The atoms band together in domains, and when a piece of iron comes near a magnet, the domains align to point in the same direction, and we see the invisible force of magnetism. Although natural magnets such as lodestone exist, most magnets today are man-made through processes that cause the domains to align and point in the same direction. Learn more about the atomic science behind magnets.

Magnetic forces are strongest at the ends of magnets. The two ends are called poles. Each magnet has a north pole (N) and a south pole (S). If you chop a magnet in half, you get two smaller magnets, each with a north and a south pole. You will never find a magnet with just a south pole or just a north pole.

If you bring a north pole of one magnet to the south pole of another magnet, they attract and will stick together. However, if you bring two north poles or two south poles together, they repel and the magnets push each other away. In other words: Unlike poles attract, Like poles repel. You can put the same poles of two bar magnets together and feel the invisible force pushing them apart. But when you turn one of those magnets the other way, you can feel the attraction as the two magnets stick together.

Some ferromagnetic materials can be permanently magnetized through processes that include mixing, heating and cooling. These permanent magnets, such as refrigerator magnets and bar magnets we use at school, do not lose their magnetic properties.

Temporary magnets can be created when they come into contact with permanent magnets, but they do not retain their magnetism. For example, if you rub a piece of iron along an existing magnet, within the iron's atoms the electrons align in a north-south direction and the iron becomes a temporary magnet. It will behave as a magnet and attract other ferromagnetic metals. If one paper clip is hung from a magnet, a second paper clip can be hung from the first, and a third from the second. However, when the magnet is removed, the paper clips will no longer act as magnets.

Magnetic Fields

Every magnet creates an invisible magnetic field around it. The area around the magnet that exerts magnetic force is known as the magnetic field. Suppose you put a bar magnet on a table and put a paper clip nearby. If you push the magnet slowly toward the paper clip, there comes a point where the paper clip jumps across and sticks to the magnet. Because of the magnetic field, the magnet can act at a distance, without having to touch the other object.

Magnetic objects must be inside a magnetic field to either pull away or push together, so this is why you sometimes have to move a magnet closer to see magnetic action happen. Magnetic fields becomes weaker with distance. To become magnetized, another magnetic substance must enter the magnetic field of an existing magnet.

Some magnetic fields are weak, while others are strong. We measure a magnetic field at a certain location by its strength and by the direction it points. When one magnet is brought close to another magnet, it is responding to the magnetic field of the second magnet. The strength and the direction of that magnetic field determines how the first magnet will behave - whether it will be attracted or repelled. So the magnetic field can create a force that can pull two magnets together or push them apart.

You cannot see a magnetic field, but you can observe its effects. If you sprinkle iron filings around a magnet, you will see them align themselves near the two poles, where the magnetic force is strongest. If you sprinkle iron filings on a sheet of paper and place a magnet under the sheet of paper, the iron filings will arrange themselves on the paper into 'lines of force', showing the magnet's magnetic field.

We usually illustrate magnetic field lines as curved lines pointing away from the north pole of the magnet and towards the south pole. These field lines are closed paths, like rubber bands, that repeat over and over. The field lines are shown closer together where the magnetic force is the strongest (at the poles). Learn more about magnetic field lines.

Magnetic fields can penetrate through all kinds of materials, not just air. When the magnets on your refrigerator hold up notes, you can see that magnetic fields go through paper. The forces of magnetic fields can extend through water, metal, cloth, and even your skin!

Earth is a Giant Magnet

The biggest magnet in the world is the one you are standing on right now! At the earth's center, its outer core is composed of moving liquid iron that makes the earth a giant magnet. The movement generates a magnetic field around the planet that extends into space. If we were to draw the Earth's field lines, they would be closest together at the poles of the giant magnet: The North Pole and South Pole.

Diagram courtesy of NASA

The magnetic north pole is slightly different from the geographic North Pole, or the earth's axis of rotation. In fact, the magnetic poles keep moving, due to activity far beneath the earth's surface. Currently the magnetic north pole is about 600 miles from the geographic pole. The yearly motion of the poles is about 25 miles per year.

Diagram of solar wind and magnetosphere courtesy of NASA
Aurora Borealis or "Northern Lights"

The magnetosphere is the earth's magnetic force that extends into space. It wraps around the earth and its atmosphere. The magnetosphere acts like a shield, protecting the earth from harmful solar wind that could damage the atmosphere and life on Earth. However, sometimes these energetic particles from the sun do interact with Earth's magnetic field, producing amazing auroras in the sky, often referred to as the Northern or Southern lights. Learn more about earth's magnetism from NASA.

The earth's magnetic field is the reason a compass works. A compass is a small device containing a magnetic needle that lines up with Earth's magnetic poles. The north-seeking pole of the needle points toward the earth's north pole. A compass comes in handy if you lose your way in the woods!

Some animals, such as pigeons, bees, salmon and whales, use Earth's magnetic field to help them navigate when migrating. Scientists aren't sure how they do this, but one theory is that these creatures have magnetic material in their bodies that acts like a compass.

Electromagnets

Another type of magnet is created when electricity passes through a wire. These magnets are called electromagnets. About 200 years ago, scientists discovered that electricity and magnetism are close cousins. An electrical current produces a magnetic field, and a moving magnet makes an electric current.

When electricity passes through a copper wire it creates a magnetic field around the wire. By winding a coil of copper wire around an iron core, the strength of the magnetic field is increased and an electromagnet is created. You can create an electromagnet at home by wrapping wire around an iron nail and using a battery to make an electric circuit. Test it out, and you'll find that the wire-wrapped nail has become a magnet.

Electromagnets are not permanent magnets. Their magnetism disappears when the current is turned off. They are temporary magnets that can be turned off by removing the electricity. For example, when you press the button of an electric doorbell, you make an electromagnet which attracts a small hammer to the chime. The electric circuit is broken when the button is not being pressed. Unlike a permanent magnet, the strength of the magnetic field of an electromagnet can be increased by increasing the amount of electric current that is used. The poles of an electromagnet can also be reversed by turning the battery around and reversing the flow of the current.

courtesy National High Magnetic Field Laboratory

Electromagnets are used in headphones, alarm systems, and loudspeakers. In your home, nearly every electric appliance with an electric motor in it uses magnets to turn electricity into motion. Motors use the forces produced by magnetic fields to produce a turning motion. This spinning motion drives all kinds of machines, from your electric toothbrush to your ceiling fan.

Just as electricity can create magnetism in an electromagnet, the movement of magnets in a generator can produce electricity. All power plants use fuel to spin magnets inside coils of wire, producing electrical current. Large electromagnets are used to generate electricity at hydroelectric dams, or with other power sources such as wind and steam.

Electromagnets can be far stronger than the permanent magnets we are familiar with. Scientists measure magnetic strength in units called tesla and gauss. One tesla equals 10,000 gauss. A refrigerator magnet is about 10 gauss. The Earth's magnetic field is about half of one gauss. The most powerful permanent magnets available, often used in medical equipment, produce fields about 1.5 tesla. But electromagnets can be much stronger, up to 30 tesla or more.

Using Magnets

Magnets are used in science, industry, and everyday life. At home, magnets hold your refrigerator door closed and make your computer speakers work. They are used in nearly all machines that use electric motors, such as vacuum cleaners and electric fans. We owe a lot to magnets! Learn more about magnets used in the home.

Magnets can be microscopic, or can weigh as much as several tons. Huge magnets separate metals at recycling centers. In scrap yards, some electromagnets are strong enough to lift a car. The mining industry uses magnets to separate iron ore from rock. Farmers use cow magnets in the stomachs of cows to trap metal that cows may have swallowed. NASA uses magnets in its spacecraft. A few countries have developed magnetically levitated trains, or maglev trains, where the high-speed trains float over tracks using repulsion forces of electromagnets. Magnets are also used in hundreds of items that we take for granted every day, including microwaves, medical equipment, power tools, wind turbines, cell phones, credit cards, treadmills, and computers. Find more uses for magnets.

Scientists continue to investigate magnetism and to develop new uses for magnetic properties. Maybe someday you will become a magnet scientist!

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