Magnetism

77

Magnetism

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The Discovery of Magnetism

Legend has it that Magnes was
herding his sheep in an area of
Northern Greece called Magnesia,
about 4,000 years ago.

The most popular legend accounting for the discovery of magnets
is that of an elderly Cretan shepherd named Magnes.

What do you think was special about that rock?

Suddenly both the nails in his
shoes and the metal tip of his
staff, became firmly stuck to
the large black rock on which
he was standing.

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To find the source of attraction he dug up the Earth to find lodestones
(load = lead or attract).
Lodestones contain magnetite, a natural magnetic material Fe3O4.

This type of rock was
subsequently named magnetite,
after either Magnesia or Magnes
himself.

Magnetic Rocks?

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What is Magnetism?

Magnetism is a class of physical phenomena that includes forces
exerted by magnets on other magnets.

It has its origin in electric currents.

Multiple Choice

27 Magnetism is a _________ force.

• Contact

• Field

• Neither

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27 Magnetism is a _________ force.

A contact

B field

C neither

Answer

*many people assume magnets are a

contact force since they can "stick"

to each other, but you can actually

feel a magnetic force through a "field" (space)

before contact even happens

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William Gilbert

William Gilbert made 2 profound discoveries: Earth was a giant magnet
and also that magnets could be produced by beating wrought iron!

A scientist named William Gilbert
is given credit to understanding
magnetism.

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Magnetic Domains

A magnetic domain is a microscopic region within a magnetic material
which has uniform magnetization.

This means that the individual
magnetic regions of the atoms
are aligned with one another
and they point in the same
direction.

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Non­Magnetized Substances

If the magnetic domains (microscopic magnetic regions) are randomized,
the substance will have no overall magnetic properties.

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Magnetized Substances

If the magnetic domains (microscopic magnetic regions) are aligned, the
substance will have overall magnetic properties and act as a magnet.

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Permanent Magnets

Materials that can be
magnetized, which are also the ones
that are strongly attracted to a
magnet, are called
ferromagnetic.

A permanent magnet is an object made from a material that is
magnetized and creates its own persistent magnetic field.

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Ferromagnetic Substances

These include iron, nickel, cobalt, some alloys of rare earth metals, and
some naturally occurring minerals such as lodestone.

On the periodic table of Elements, these 3 elements are grouped together.
Is this just a coincidence?

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Temporary Magnets

Temporary Magnets simply act like permanent magnets when they are
within a strong magnetic field.

Unlike permanent magnets however, they loose their
magnetism when the field disappears. Paperclips, iron nails
and other similar items are examples of temporary magnets.

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Un­Magnetized Iron­
Domains are random

Magnetized Iron­
Domains are aligned

Magnetizing an Iron Nail

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Electromagnets have a soft metal core made into a magnet by the

passage of electric current through a coil surrounding it.

Unlike permanent magnets however, they lose their

magnetism when the current disappears.

Electromagnets

Multiple Choice

28 Michael Faraday discovered Earth was a giant magnet.

• True

• False

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28 Michael Faraday discovered Earth was a giant
magnet.

True

False

Answer

It was William Gilbert

Multiple Choice

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29 Microscopic regions inside iron are called:

• magnetic crystals

• magnetic domains

• magnetic atoms

Multiple Choice

30 Ferromagnetics substances include: all but

• Iron

• Aluminum

• Nickel

• Cobalt

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30 Ferromagnetics substances include:
(select all that are ferromagnetic)

A

iron

B

aluminum

C

nickel

D

cobalt

Answer

Multiple Choice

1 An electromagnet produces a magnetic field when current stops flowing through it.

• True

• False

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31 An electromagnet produces a magnetic field when
current stops flowing through it.

True

False

Answer

No, it needs the current to be magnetized. So

when the current stops so does it's magnetic field.

Multiple Choice

32 Soft Iron is an example of________________.

• an electromagnet

• a temporary magnet

• a permanant magnet

• a superconductor