electromagnetism and magnetic circuit 2
TRANSCRIPT
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ElectromagneticInduction
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Electromagnetic Induction
Voltage is induced whether the magnetic field of a
magnet moves near a stationary conductoror
the conductor moves in a stationary magnetic
field.
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Demo: Magnet Induces Current
Voltage is induced when a magnet moves towards
or away from a coil, inducing a current in the coil.
Faster the magnets motion, the greater the
induced current.
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Magnetic Recording
Write data by magnetizing
recording media (e.g.,
video tape, hard disk)using electromagnets.
Data is read back using the
induced current produced
when magnetized mediamoves past receiver coils
(reverse of writing data).Hard disk
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Electric Generator
Electric generator moves a conductor in a
magnetic field to produce voltage via
electromagnetic induction
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Demo: Electric Generator
Turn the shaft byhand and as
the coils passthe magnets avoltage isinduced.
DC current isgenerated.
Magnet
Magnet
Coils
DC Output
S
HA
F
T
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Induction: No Free Lunch
Takes work to turn
the generator crank
to produce electriccurrent.
The faster we turn
the crank to
produce morecurrent, the more
difficult it is to turn.
More difficult topush the magnetinto a coil with
more loopsbecause themagnetic field ofeach current loopresists the motionof the magnet.
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Faradays Law
The induced voltage in a coil is proportional to the
product of the number of loops and rate at which
the magnetic field changes within the loops.
Small
Voltage
Medium
Voltage
Large
Voltage
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Self-Induction
When a current is
induced by a
changing magneticfield, that current
itself produces its
own magnetic field.
This effect is calledself-induction.
Current
Primary Magnetic Field
Self-Induced
Magnetic Field
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Demo: Magnetic Brakes
Strong magnet dropped into
a copper pipe falls slowly
due to secondary magneticfield induced by its motion.
Great AmericasDrop Zone
has a 22 story freefall,
lasting four seconds,
decelerated by magnetic
braking.
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Eddy Currents
Changing magnetic field
induces eddy currents
within any conductor.
These internal currents
produce self-induced
magnetic fields, which
by Lenzs law are in
opposition of theprimary magnetic field.
Eddy
Currents
Primary Magnetic Field
Self-Induced
Magnetic Field
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Metal Detectors
Can detect the presence ofmetals by using atransmitter coil to create
an oscillating primarymagnetic field.
This creates a secondarymagnetic field due to eddycurrents in the metal.
Can detect this secondarymagnetic field by using areceiver coil.
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Demo: Back Electromotive Force
Changing magnetic field in an electromagnet
induces a voltage in the electromagnet
itself.
When we disconnect a large
electromagnet the magnetic field
rapidly collapses.
This changing magnetic field
self-induces a large voltage in the
coil of the electromagnet.
Large spark occurs at the switch.