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6) Magnetism & Electromagnetism (Magnetic field lines (Uniform Fields,…
6) Magnetism & Electromagnetism
Magnetic field lines
All Magnets have two poles - north and south
A
magnetic field
is a
region
where
magnetic materials
experience a
force
magnetic field lines
are used to show the size and direction of magnetic fields
they always point from
North
to
South
Uniform Fields
Placing the north and south poles of two permanent bar magnets near each other creates a
uniform field between
the two magnets
experiments to investigate magnetic fields
put magnets under a piece of paper and scatter the iron filings on top.
you can also use multiple compasses to see the magnetic field lines coming out of a bar magnet or between two bar magnets
current carrying wire creates a magnetic field
an electric current in a material produces a magnetic field around it.
the larger the electric current, the stronger the magnetic field
the direction of the magnetic field depends on the direction of the current
current in a magnetic field creates a force
when a current carrying wire is put between magnetic poles, the two magnetic fields affect one another. the result is a force on the wire. this can cause the wire to move
the motor effect
the wire has to be at 90* to the magnetic field
If there is a wire- with a current running through- in a magnetic field it will experience a force ie it will be pushed up or down.
Electric motors
In a DC motor, there is a wire in a magnetic field. The force it experiences turns it around, this turns a 'split ring commutator' this basically is where charge goes from 'brushes' into the wires
Loudspeakers
In a loud speaker, a coil is in a magnetic field. When a current is run through it the wire will experience a force that pushes it away from the field, this in turn pushes a cone which makes the sound. Whatever frequency the AC current is at, the coil will move at that frequency, making a note of a certain pitch.
If you have a wire in a magnetic field, if you increase the current there will be more force on the wire; if you increase the strength of the magnetic field there will be more force on the wire.
Fleming's Left hand rule
Using your left hand, point your
F
irst finger in the direction of the
F
ield and your se
C
ond finger in the direction of the
C
urrent.
Your thu
M
b will then point in the direction of the force (
M
otion)
