Download Magnetism

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
• Man-made magnets: most are made from
iron, steel, nickel, cobalt
• Magnetic substances are materials that
are attracted to a magnet
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)
• 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
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
Making a magnet
stroke bar of magnetic material in one
direction with a magnet (re-aligns
domains)
use electricity
bring magnet nearby (if soft iron)
How to demagnetize a magnet
heat
contact (pass magnet alternating direction)
hammering
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)
3 things needed to make
electromagnet:
soft iron bar (core)
coil of insulated wire
source of electric current
• How to change strength of electromagnet
 varying the number of turns of wire around
core
 increasing the current
 varying the thickness of core
 change core material (if use wood = no
electromagnet, use cobalt = strength
increased 170 times, but if you use iron =
strength increased 1000 times)
۩ Electromagnet summary
magnetic field around straight wire that
carries current
bending wire into loops causes each loop
to act as a separate magnet
adding more coils increased strength of
electromagnet
increasing number of electrons through
wire increases strength of electromagnet
larger and thicker iron core provides more
magnetic domains = increases strength of
electromagnet
Useful Vocabulary
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Static electricity
Volts
Amps
Ohmns
V=I x R
Electricity
Circuits
Parallel
Series
Alternating Current
Direct Current
Insulators
Conductors