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Magnetism

by Ron Kurtus (revised 6 October 2006)

Magnetism is a force that acts at a distance due to a magnetic field. This field is caused by moving electrically charged particles or is inherent in magnetic objects such as a magnet. A magnet is an object that exhibits a strong magnetic field and will attract materials like iron to it. Magnets have two poles, called the north (N) and south (S) poles. Two magnets will be attacted by their opposite poles, and each will repel the like pole of the other magnet. Magnetism has many uses in modern life.

Questions you may have include:

• What is a magnetic field?
• What are magnets?
• How is magnetism used?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Useful tools: Metric-English Conversion | Scientific Calculator.

Magnetic field

A magnetic field consists of imaginary lines of flux coming from moving or spinning electrically charged particles. Examples include the spin of a proton and the motion of electrons through a wire in an electric circuit.

What a magnetic field actually consists of is somewhat of a mystery, but we do know it is a special property of space.

Magnetic field or lines of flux of a moving charged particle

Names of poles

The lines of magnetic flux flow from one end of the object to the other. By convention, we call one end of a magnetic object the N or North-seeking pole and the other the S or South-seeking pole, as related to the Earth's North and South magnetic poles. The magnetic flux is defined as moving from N to S.

Magnets

Although individual particles such as electrons can have magnetic fields, larger objects such as a piece of iron can also have a magnetic field, as a sum of the fields of its particles. If a larger object exhibits a sufficiently great magnetic field, it is called a magnet.

(See Magnets for more information.)

Magnetic force

The magnetic field of an object can create a magnetic force on other objects with magnetic fields. That force is what we call magnetism.

When a magnetic field is applied to a moving electric charge, such as a moving proton or the electrical current in a wire, the force on the charge is called a Lorentz force.

(See Magnetism and the Lorentz Force for more information.)

Attraction

When two magnets or magnetic objects are close to each other, there is a force that attracts the poles together.

Force attracts N to S

Magnets also strongly attract ferromagnetic materials such as iron, nickel and cobalt.

(See Magnetic Materials for more information.)

Repulsion

When two magnetic objects have like poles facing each other, the magnetic force pushes them apart.

Force pushes magnetic objects apart

Magnets can also weakly repel diamagnetic materials. (See Magnetic Materials for more information.)

Magnetic and electric fields

The magnetic and electric fields are both similar and different. They are also inter-related.

Electric charges and magnetism similar

Just as the positive (+) and negative (-) electrical charges attract each other, the N and S poles of a magnet attract each other.

In electricity like charges repel, and in magnetism like poles repel.

Electric charges and magnetism different

The magnetic field is a dipole field. That means that every magnet must have two poles.

On the other hand, a positive (+) or negative (-) electrical charge can stand alone. Electrical charges are called monopoles, since they can exist without the opposite charge.

Summary

Magnetism is a force that acts at a distance and is caused by a magnetic field. The magnetic force strongly attracts an opposite pole of another magnet and repels a like pole. The magnetic field is both similar and different than an electric field.

Answers to Readers' Questions

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Resources

The following resources provide information on this subject:

Websites

Explanation of Magnetism - from NASA

Magnetism - from South Dakota School District

Physical Science Resources

Books

Top-rated books on Magnetism

Miscellaneous

Mini-quiz to check your understanding

1. What does the movement of an electric charge cause?

2. What happens when two objects with magnetic fields are brought near each other?

3. Is a magnet a dipole or monopole?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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