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, such as iron, steel, nickel, and cobalt. Magnets can either attract or repel other magnets, which makes them very useful in everyday life.

One common example of a magnet is the small magnet stuck to a refrigerator door to hold notes or pictures. These are called permanent magnets because they stay magnetized all the time. Permanent magnets are made from special materials, like alnico or ferrite, that keep their magnetic properties even without an external force.

Another type of magnet is called an electromagnet. This kind of magnet is made by running an electric current [/w/19] through a coil of wire. When the current flows, the coil becomes magnetic, but when the current stops, the magnetism disappears. Electromagnets are often used in machines and devices where controllable magnetism is needed, such as in motors and computers.

Discovery and development

Main article: History of electromagnetic theory

See also: Magnetism history

Long ago, people discovered magnetism from special rocks called lodestones or magnetite. These rocks could attract iron and were used to make the first magnetic compasses. Early records of magnets come from places like Anatolia, India, and China over 2,500 years ago.

Later, people found that heating iron and letting it cool in the direction of Earth's magnetic field could make it a permanent magnet. This helped create better compasses for navigation. Over time, scientists like Hans Christian Ørsted and Joseph Henry discovered how electric currents could create magnetic fields, leading to the development of powerful electromagnets.

Physics

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

Magnets have two ends called poles — a north pole and a south pole. Opposite poles attract each other, while similar poles repel. The Earth itself acts like a giant magnet, with its magnetic north pole near the geographic north pole. Certain materials, like iron and steel, can become magnets or be attracted to them, while others, like plastic or wood, are not affected by magnetic fields.

Common uses

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

Older televisions and computer monitors used a special type of magnet to control the display. Magnets are also important in sensors, speakers, and microphones, helping to turn electrical signals into sound and vice versa. Electric guitars use magnetic pickups to turn string vibrations into electrical signals.

In medicine, magnetic resonance imaging uses strong magnets to see inside the body without surgery. Compasses are magnets that point toward Earth's magnetic field to show direction. Magnets are also fun in toys, like the Magnet Space Wheel and Levitron, and can be used to hold notes on refrigerator doors or to make jewelry.

Medical issues and safety

Further information: Electromagnetic radiation and health

Most scientists agree that static magnetic fields, like those from regular magnets, do not harm health. However, moving magnetic fields might be different, and some people wonder if they could be linked to health issues like cancer.

There are some special safety concerns with magnets. If someone has a pacemaker—a small device placed in the chest to help the heart work—it can be affected by strong magnetic fields. For this reason, people with pacemakers should avoid places with strong magnetic fields, like rooms with MRI machines.

Children can sometimes swallow small magnets from toys, which can be dangerous if more than one magnet is swallowed. The magnets can harm internal body tissues. Also, rooms with powerful MRI machines are kept free of metal objects because the strong magnetic fields can throw metal items around.

Magnetizing ferromagnets

See also: Remanence

Ferromagnetic materials can become magnets in several simple ways. One way is to heat the material above a special temperature called the Curie temperature, let it cool while inside another magnetic field, and tap it gently as it cools. This method works very well and is used to make strong permanent magnets.

Another way is to place the object inside a magnetic field — after you take it out, it may stay somewhat magnetic. Moving it while it’s vibrating can help it keep more magnetism. You can also magnetize something by stroking it with another magnet, moving the magnet along the object in one direction again and again. Finally, running an electric current through a coil near the object can line up its tiny magnetic parts, making it magnetic too.

Demagnetizing ferromagnets

Magnetized materials can lose their magnetism in several ways. One way is by heating them past a special temperature, called the Curie temperature, which causes their magnetic properties to disappear. Another method involves using an alternating magnetic field, which can be used to demagnetize tools, erase credit cards, or wipe data from hard disks.

Mechanical shocks, like hammering, can also disrupt the alignment of magnetic domains and reduce magnetization, though this might damage the object.

Types of permanent magnets

Many materials can act as magnets because of the way tiny particles inside them, called electrons, behave. Some metals, like iron ore, cobalt, and nickel, are naturally magnetic. These metals have been used since the earliest studies of magnetism.

Today, we also make magnets from mixtures of materials. For example, ceramic magnets are made from a mix of iron oxide and other materials, making them inexpensive and easy to shape. There are also special magnets called rare-earth magnets, made from elements like samarium–cobalt and neodymium–iron–boron (NIB), which are very strong but more expensive. Each type of magnet has its own uses, depending on how strong it needs to be and how much it costs.

Main article: Rare-earth magnet

Main article: Single-molecule magnet

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. Wrapping the coil around a special material, like an iron nail, can make the magnetic field much stronger.

Electromagnets are used in many important machines, such as particle accelerators, electric motors, junkyard cranes, and magnetic resonance imaging machines. They can also be designed in special shapes to control the path of particles in science experiments.

Units and calculations

Magnets have special properties because of an invisible force called a magnetic field. This field can pull or push certain metals like iron and can attract or repel other magnets.

Scientists use different units to measure these magnetic properties. The most common units are called SI units, but physicists often use other units too. There are two main types of magnetic fields scientists study: one called B and another called H. These fields help explain how magnets work and how they can move or affect other objects.