The Modern Principia

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Magnets FAQ

Magnetism is one of the most fascinating topics in physics, but one of the least understood. Here’s a little FAQ to answer some common questions about magnetism. 

• What exactly is a magnet?

A magnet is defined as an object that has both a north and south pole, and that can create a magnetic field. Easily magnetized materials, such as iron, steel, nickel and cobalt have atoms arranged in small units, called domains. Each domain contains trillions of atoms and acts like an individual magnet. If the magnetic material is placed in a strong magnetic field,  the individual domains will generally swing around in the general direction of the field. When most of the domains are aligned to the field, the material becomes a magnet. 

Before magnetization:
 
After magnetization: 

• What do magnets actually do? 

Magnets attract objects via a magnetic force on other ferromagnetic objects - some notable ones include objects composed of iron, nickel and cobalt. Magnets are also able to effect electrically charge particles and conductors. Because of these interesting properties, magnets are able to convert electrical energy to mechanical energy and vice-versa. Magnetism exists due to the motion of the electrical charges within the atomic structure of these materials.

• What’s the difference between a “permanent” magnet and “electromagnet?”

Permanent magnets continuously emit a magnetic force, even in the absence of a power source. On the other hand, electromagnets require a power source in order to generate a magnetic field. Permanent magnets retain their magnetism unless affected by a strong outside magnetic/electrical force or extremely high temperature. Permanent magnets will lose their own magnetism eventually, but at an extremely slow rate - on the order of one percentage point every decade. 

• How is a magnet’s polarity determined? 

If allowed to move freely and not under a strong force, a magnet will naturally align itself with the north-south polarity of the Earth. 

• How are magnets made? 

Modern magnet materials are made through casting, pressing and sintering, compression bonding, injection molding, extruding, or calendaring processes.

• What are superconductors? 

Superconductors are the strongest type of magnets. They don’t require a metal core, but are made of coils of wire made from special metal alloys cooled to very low temperatures. Superconductors have zero electrical resistance, which makes an electrical current flow very easily. 

• How do lines of magnetic flux behave? 

Lines of force are three-dimensional, surrounding a bar magnet on all sides.

However, it is much simpler to think of them as two dimensional. Like poles repel and unlike poles attract. When opposite poles of a magnet are brought together, the lines of force join up and the magnets pull together.

When like poles of a magnet are brought together, the lines of force push away from each other and the magnets repel each other.