UNIT 7: Từ tính

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Nội dung Text: UNIT 7: Từ tính

LOGO www.themegallery.com Magnetism
LOGO Magnet The first magnets were known as magnetite or loadstone.
LOGO Magnetic field lines of a bar magnet
LOGO Magnet Iron filings "map" of the field of a bar magnet
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LOGO 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. June 6, 2011
LOGO Making Magnets Stroking a piece of unmagnetised iron or steel with a known magnet can make it into a magnet.
LOGO Making Magnets Placing a magnet alongside a non- magnetised steel knitting needle for some time will magnetise it.
LOGO The Earth – A huge magnet
LOGO Electric current and magnetism
LOGO 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.
LOGO Ferromagnetic material
LOGO Spinning electrons
LOGO Domains Magnetic material with domains misaligned Aligned domains makes material highly magnetic
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LOGO Non magnetic material
LOGO Permanent magnet
LOGO Demagnetize Heating a piece of magnetized iron or steel strongly in a flame will demagnetize it.
LOGO Solenoid H = NI/ L