Magnet

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but creates a force that pulls on certain metals like iron, steel, nickel, and cobalt. One common example of a magnet is the refrigerator magnet that holds notes to a fridge door.

Permanent magnets are made from special materials that stay magnetized for a long time. These materials include alloys like alnico and ferrite. They are treated in strong magnetic fields during production to keep their magnetic strength.

An electromagnet is different. It is created by running an electric current through a coil of wire. When the current flows, the coil becomes magnetic, but it stops being a magnet when the electricity stops. Electromagnets are often used with a core of soft metal like mild steel to make their magnetic field stronger.

Magnets are important in many everyday items, from the refrigerator magnet on your fridge to the motors in fans and computers. They help us understand forces and are used in many technologies that make our lives easier.

Discovery and development

Main article: History of electromagnetic theory

See also: Magnetism history

Ancient people discovered magnetism from lodestones or magnetite, which are naturally magnetized pieces of iron ore. The word magnet comes from the Greek word for a stone from Magnesia, a place in Anatolia (now Manisa in Turkey). These early magnets were used to make the first magnetic compasses.

Later, people learned that heating iron and letting it cool in the direction of Earth's magnetic field could make it a permanent magnet. This discovery helped create better compasses for navigation. Over time, scientists like Hans Christian Ørsted, André-Marie Ampère, William Sturgeon, and Joseph Henry found new ways to create and strengthen magnets using electricity.

Physics

A magnet is a special material that produces an invisible force called a magnetic field. This field can pull certain metals like iron and steel toward it, or it can push other magnets away. The strength and direction of this force depend on the magnet’s shape and the way it’s made.

Magnets have two ends called poles—a north pole and a south pole. Opposite poles attract each other, while similar poles push away. For example, the north pole of one magnet will pull toward the south pole of another magnet. The way magnets behave helps us understand many everyday tools, from fridge magnets to the compasses we use for direction.

Common uses

Magnets are used in many everyday items and technologies. For example, VHS tapes, audio cassettes, floppy disks, and hard disks all use magnetic tape or coatings to store information. Similarly, credit and debit cards have a magnetic strip that holds your account information.

Magnets are also found in many electronic devices. Older televisions and computer monitors used a special type of magnet to control the screen display. Speakers and microphones use magnets to help convert electrical signals into sound and vice versa. Electric guitars use magnetic pickups to turn string vibrations into electrical signals.

In industry and medicine, magnets have important uses too. Magnetic resonance imaging uses very strong magnets to take detailed pictures of the inside of the body without surgery. Chemists use a similar technique called nuclear magnetic resonance to study materials.

Magnets are also used in many tools and toys. Refrigerator magnets are a common household item, and magnets are used in many children's toys to create fun effects. Some compasses use a small magnet to point toward the Earth's north pole.

Medical issues and safety

Further information: Electromagnetic radiation and health

Most scientists agree that static magnetic fields, like those from ordinary magnets, do not harm health. However, strong changing magnetic fields might be a concern, and some studies have looked at whether they could affect health.

There are some safety issues with magnets. If a person has a pacemaker to help their heart, strong magnets can interfere with it. That’s why people with pacemakers should stay away from big magnetic machines like MRIs.

Swallowing small magnets can be dangerous, especially if more than one is swallowed, as they can hurt inside the body. Also, rooms with strong magnets, such as those used in medical imaging, must keep out metal objects, because the magnets can throw them around powerfully.

Magnetizing ferromagnets

Ferromagnetic materials, like iron, can become magnets in several simple ways. One way is to heat the material past a special temperature called the Curie temperature, let it cool while a magnet is nearby, and then tap it gently as it cools. Another method is to place the material inside a magnet’s field — it will keep a bit of that magnetism even after you take it away. Moving a magnet along the material in one direction, or using electric current to create a magnetic field, can also make it magnetic.

Demagnetizing ferromagnets

Ferromagnetic materials, which are materials that can become magnets, can lose their magnetism in several ways. One way is by heating them past a special temperature called the Curie temperature, which messes up the arrangement of tiny magnetic areas inside the material. Another method is using a special alternating magnetic field, which can be used to erase information from things like credit cards or hard disks.

Additionally, if a magnet is hit or shaken hard enough, it can lose some of its magnetism because the internal magnetic areas get mixed up. However, this can also damage the object.

Types of permanent magnets

Many materials can act as magnets because their tiny particles, called electrons, can spin in ways that create magnetic effects. Some metals, like iron, cobalt, and nickel, are naturally magnetic. These metals can be used to make simple magnets, like the ones you might stick on your fridge.

There are also man-made magnets created by mixing magnetic metals with other materials. For example, some magnets are made from a mix of iron oxide and certain ceramics, which makes them strong but also somewhat brittle. Other magnets are made by mixing metals together, like aluminium, nickel, and cobalt, which creates magnets that resist rust and keep their shape well. Scientists are always finding new ways to make stronger and more useful magnets.

Electromagnets

Main article: Electromagnet

An electromagnet is made by coiling a wire into loops, called a solenoid. When electricity flows through the wire, it creates a magnetic field, similar to that of a regular magnet. The strength of this magnetic field depends on how many loops of wire are used, the size of the loops, and how much electricity flows through the wire.

Wrapping the coil around a special material, like an iron nail, can make the magnet much stronger. Electromagnets are used in many important machines, such as particle accelerators, electric motors, junkyard cranes, and magnetic resonance imaging machines.

Units and calculations

Magnets can be measured using different units, but two main types are commonly used: SI units and Gaussian units. These units help scientists and engineers understand how magnets work.

There are two important magnetic fields to know about:

• B, which shows the strength of the magnetic field. It’s measured in teslas (T) in SI units.
• H, which tells us about the magnetic field created by electric currents. It’s measured in ampere-turns per meter (A-turn/m) in SI units.

These fields help explain how magnets attract or repel each other and how they can affect moving electric charges.