MAGNETISM

Chapter 22

Magnetism

Magnetism is a force of attraction or repulsion due to an arrangement of electrons

The Magnetic forces usually are strongest at the two ends of the magnet. These are called poles

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Poles

The end of the magnet that points toward the north is called the north magnetic pole. The other end that points south is the south magnetic pole.

The rule for magnetic poles is: Like poles repel, unlike poles attract

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Magnetic Fields

The region in which magnetic forces can act is called a magnetic field

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Magnetic Materials

Natural magnets – naturally occurring substances that have magnetic properties. ex: magnetite.

Magnetic induction – the process by which a material is made into a magnet. ex: stroking some materials in one direction with a strong magnet

Temporary magnets – materials that are easy to magnetize, but lose their magnetism quickly. ex: soft iron

Permanent magnets – materials that are more difficult to magnetize, but tend to stay magnetized. ex: cobalt, nickel and iron

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Magnetic Materials cont.

Why are some materials magnetic while others aren’t?

Scientists believe that magnetism is due to the motion of electrons- particularly their spin.

All electrons spin and create a magnetic field around themselves.

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Magnetic Materials cont.

Most electrons occur in pairs with opposite spins which cancel each others magnetic fields. Some metals contain electrons with unpaired electrons.

A region in which the magnetic fields of atoms are grouped together is called magnetic domain. The domains are randomly arranged in an un-magnetized object.

In a magnetized object the domains are aligned.

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Electromagnetism Electricity and magnetism are related. This

is called electromagnetism An electric current flowing through a wire

gives rise to a magnetic field whose direction depends upon the direction of the current.

Coiling a conductor around a piece of soft iron will produce a powerful magnet. This is temporary and is only magnetic as long as current passes through the wire

The strength of an electromagnet can be increased two ways:

↑ the number of loops ↑ the voltage

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Electromagnetic Induction

English scientist Michael Faraday discovered that electric current could be generated or induced by moving a wire through a magnetic field

The process by which a current is produced by the motion of a conductor (wire) in a magnetic field is called electromagnetic induction

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