UNIT 7: Từ tính ppt

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Magnetism

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Magnet
The first
magnets
were
known as
magnetite
or
loadstone.

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Magnetic field lines of a bar magnet

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Magnet
Iron filings "map" of the field of a bar magnet

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July 29, 2014
Cutting a magnet

An interesting characteristic of magnets is that
when you cut a magnet into parts, each part will
have both N and S poles.

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Making Magnets
Stroking a
piece of
unmagnetised
iron or steel
with a known

magnet can
make it into a
magnet.

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Making Magnets
Placing a magnet alongside a non-
magnetised steel knitting needle for some
time will magnetise it.


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The Earth – A huge magnet

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Electric current and magnetism

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Classification of materials

Ferromagnetic materials

strongly attracted by a magnetic force:
iron (Fe), nickel (Ni), cobalt (Co) and
gadolinium (Gd)

Paramagnetic materials

weakly attracted to magnets: Aluminum

Diamagnetic materials

when they are exposed to a strong
magnetic field, they induce a weak
magnetic field in the opposite direction.

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Ferromagnetic material

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Spinning electrons

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Domains
Magnetic material with domains misaligned
Aligned domains makes material highly magnetic

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Non magnetic material

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Permanent magnet

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Demagnetize
Heating a piece of
magnetized iron or
steel strongly in a
flame will
demagnetize it.

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Solenoid
H = NI/ L