Download Electricity and Magnetism

Electricity and
Magnetism
Section 8.2
Moving charges and magnetic
fields
Moving charges, like those in an electric
current, produce magnetic fields
The magnetic field around a currentcarrying wire forms a circular pattern about
the wire
The direction of the field depends on the
direction of the current
Moving charges and magnetic
fields
The strength of the magnetic field depends
on the amount of current flowing in the
wire
Electromagnet- a temporary magnet made
by placing a piece of iron inside a current
carrying coil of wire
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http://www.howstuffworks.com/electromagnet.
htm
http://ithacasciencezone.com/midscizone/phy
sical/p04magnetism/magnetism/slide4.htm
Electromagnets
Magnetic field is present only when current is
flowing in the wire coil
Increase strength of the magnetic field by
adding coils to the wire or increasing the current
flowing through the wire
Magnetic properties of electromagnets can be
controlled by changing the electric current
flowing through the wire coil
Converts electrical energy into mechanical
energy to do work- like speakers!
Galvanometer
Galvanometer- a device that uses an
electromagnet to measure electric current
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Examples: gas indicator, engine light, oil temperature
Current changes as temperature changes, needle is
connected to an electromagnet, which is suspended
so it can rotate between the poles of a permanent
fixed magnet
When current flows through the coil, the
electromagnet rotates
http://www.hometrainingtools.com/articles/home
made-galvanometer.html
Electric motor
Electric motor- a device that changes
electrical energy into mechanical energy
Contains an electromagnet that is free to
rotate between the poles of a permanent
fixed magnet
The coil in the electromagnet is connected
to a source of electric current (battery,
power outlet)
Electric motor
When a current flows through the
electromagnet, a magnetic field is
produced in the coil
Changing the direction of the current
causes the coil in the electric motor of
keep rotating
Rotation speed of electric motors can be
controlled
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Vary the amount of current flowing through the
coil
Electric motors
When more current flows through the coil, the
electromagnet’s magnetic field becomes stronger
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The magnetic force between the coil and the permanent
magnet increases, and the coil turns faster
Commutators- reverse current in the coil- for DC power
sources.
AC reverses direction 120 times a second, so they don’t
need commutators
Extra info:
http://www.physclips.unsw.edu.au/jw/electricmotors.html