magnetism physical science mr. holmes. loadstones are: natural magnets found in ground contain iron...
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Magnetism
Physical Science
Mr. Holmes
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• Loadstones are:
• natural magnets found in ground
• contain iron ore (magnetite)
• earliest use as simple compass because it will align north-south
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• Man-made magnets: most are made from iron, steel, nickel, cobalt
• Magnetic substances are materials that are attracted to a magnet
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Theory of magnetism most elements electrons spin opposed to one another and magnetic forces cancel each other out but in magnetic substances this spinning motion reinforces each other (domain theory)
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• Law of magnetic poles– a magnet has the greatest strength at the
poles (little or no strength in middle)– ends are called poles (free ends)– hang bar magnet from ring stand – the bar
end pointing north = north pole
• Law of magnetic pole – like poles repel, unlike poles attract
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Force of attraction or repulsion depends on strength of magnets and distance between poles
• Magnetic field – region around a magnet in which magnetic effects are observed, which is produced by the motion of the electric charge.
• Lines of force – closed arc from north to south pole, never cross, most concentrated at poles
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Making a magnetstroke bar of magnetic material in one
direction with a magnet (re-aligns domains)
use electricitybring magnet nearby (if soft iron)
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How to demagnetize a magnetheatcontact (pass magnet alternating direction)hammering
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Electromagnets
• When electric current passes through a wire – a magnetic field is produced in the space surrounding the wire
• (electromagnet = placing soft iron bar in center of coil of wire with electricity passing through it)
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3 things needed to make electromagnet:soft iron bar (core)coil of insulated wiresource of electric current
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• How to change strength of electromagnetvarying the number of turns of wire around
core increasing the currentvarying the thickness of corechange core material (if use wood = no
electromagnet, use cobalt = strength increased 170 times, but if you use iron = strength increased 1000 times)
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۩ Electromagnet summarymagnetic field around straight wire that carries
currentbending wire into loops causes each loop to act as
a separate magnetadding more coils increased strength of
electromagnetincreasing number of electrons through wire
increases strength of electromagnetlarger and thicker iron core provides more magnetic
domains = increases strength of electromagnet
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Useful Vocabulary
• Static electricity
• Volts
• Amps
• Ohmns
• V=I x R
• Electricity
• Circuits
• Parallel
• Series
• Alternating Current
• Direct Current
• Insulators
• Conductors