Transcript Magnetism powerpoint - Tasker Milward Physics Website

COMPUTER PRESENTATIONS FOR
KS3 SCIENCE - PHYSICS
©2003, STEVE PARKER
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KS3 SCIENCE
- PHYSICS
Magnetism
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MAGNETIC FORCES & FIELDS
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MAGNETIC FORCES & FIELDS
“Magnets” are things which create
a force that attracts or repels objects
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MAGNETIC FORCES & FIELDS
“Magnets” are things which create
a force that attracts or repels objects
Only certain
magnetic
materials are
attracted by
magnets
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MAGNETIC FORCES & FIELDS
Steel can be magnetised permanently
by stroking a magnet along it
There are small
magnetic regions
or “Domains” in
the steel, which
are jumbled up
to start with
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MAGNETIC FORCES & FIELDS
Steel can be magnetised permanently
by stroking a magnet along it
Stroking with a
magnet lines-up
the domains, and
we think that this
is what makes a
thing magnetic
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MAGNETIC FORCES & FIELDS
Some metals can be magnetised, or
attracted by a magnet, others cannot
Magnetic metals
Other metals,
include iron,
wood, plastic
steel, nickel
etc. cannot be
and cobalt
attracted by
a magnet
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MAGNETIC FORCES & FIELDS
Magnets create a “Magnetic Field”
around them which runs from the
“North Pole” to the “South Pole”
N
S
MAGNETIC FORCES & FIELDS
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Magnetic forces can be felt anywhere
within the magnetic field, but poles
are the strongest parts of a magnet like poles repel, unlike poles attract
NNNN
SSSS SSSS
NNNN
NNNN
SSSS NNNN
SSSS
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MAGNETIC FORCES & FIELDS
The Earth also has a
magnetic field, going
from geographic South
to geographic North
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MAGNETIC FORCES & FIELDS
The Earth also has a
magnetic field, going
from geographic South
to geographic North
A bar magnet suspended
horizontally will align
with the Earth’s magnetic
field like a compass
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ELECTROMAGNETS
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ELECTROMAGNETS
A coil of wire with an electric
current running through it
generates a magnetic field this is called a “Solenoid”
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ELECTROMAGNETS
The coil becomes like a bar magnet
with a strong magnetic field inside
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ELECTROMAGNETS
The magnetic field is stronger if we
increase the current through the coil
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ELECTROMAGNETS
The magnetic field also becomes
stronger if the coil has more turns
ELECTROMAGNETS
The magnetic field is particularly
strong with an iron bar inside the coil
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ELECTROMAGNETS
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The end result is like a strong bar
magnet and the position of the poles
depends on the direction of the current
CURRENT
CURRENT
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USES OF ELECTROMAGNETS
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USES OF ELECTROMAGNETS
Using a solenoid with an iron
bar inside can create a very
strong magnetic force, and it
can also be switched on and off
A good example
is the use of an
electro-magnet
to pick up cars
in a scrap yard
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USES OF ELECTROMAGNETS
Other examples include bells,
which are used in schools
to herd the children around
Electro magnets
pull the arm, this
movement then
breaks the circuit
so the arm is
released again