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Magnetic Fieldsand
Electromagnetism
Created for CVCA PhysicsBy
Dick Heckathorn19 April 2K+4
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18.1 Natural Magnetism 676
Investigation
How Do Magnetic Regions
Relate To Each Other?
Magnets
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Repulsive
Repulsive
Attractive
What is the interaction force?
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Magnetic Fields
What is a magnetic field?
What is the symbol for magnetic field?
What is its usefulness?
How do we see a magnetic field?
B
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Investigation
Viewing a magnetic field
Magnets – spheres in Plexiglas
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Magnetic Field Around a Bar Magnet
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The Magnetic Field Between Unlike Poles
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The Magnetic Field Between Like Poles
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Demonstrate
1. Tie a paper clip to a string. Then move the arrow above the large magnet.
2. Which way does the field really point?
Large Magnet - Arrow
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Investigate
1. Place a magnet on a piece of paper.
2. Move a compass around the magnet keeping the compass on the paper.
Bar magnet – compass – piece of paper
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Investigate
3. Create the following.
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Investigate
4. Would this be the end result if one mapped the whole area?
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Magnetic Fields
How do we detect a magnetic field?
(compass)
What is the direction of a magnetic field?
(direction north seeking endof compass points)
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A Question
Equally huge – Newton’s 3rd Law
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A problem
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Demonstration
Which end of a magnet
points north?
2 Bar magnets – magnet holders - support
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Question
How does the
earths magnetic north pole
compare to the
earth geographic north pole?
Handout: Magnetic Declination
2 Bar magnets – magnet holders - support
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Magnetic Declination
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Demonatration
Breaking a magnet
Special magnets – compass - overhead
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Investigation
Magnetizing
a temporary magnet
using a nail
and
DC current.
Battery – nail – wire – paper clips
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18.2 Electromagnetism 681
What did Oersted discover?
Moving electric charges produce a magnetic field.
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Investigation
What exists around a current carrying wire?
How is its direction defined?
Power Source – coils of wire - compasses
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What one would see with a magnetic field viewer.
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How can one predict the direction of
the magnetic field?
Grab wire with thumb in direction of current, fingers
give direction of field.
Question
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Thumb?
Direction of current.
Fingers?
Direction of magnetic field.
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Investigation
What exists around a single coil of wire with a current in it?
carrying wire?
How is its direction defined?
Power Source – coils of wire - compasses
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Question
What is the direction of the magnetic field of a coil that has
a current in it?
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Demonstration
Bring compass
near each end
of a coil.
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How is the magnetic field of a coil related to a magnet?
Like a bar magnet
But can be turned on and off
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Quiz
Given the polarity
of the power source
and the direction the wire
is wound on the apparatus,
what is the direction of the magnetic field inside the coil?
Power Source – wire coil on PVC pipe
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18.4 Magnetic Forceson
Conductorsand
Moving Chargespage 687
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Demonstration
Force on
current carrying wire
in a
magnetic field
Green power source, large magnet, swinging wire, support
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Thumb
Direction of Current
Fingers
Direction of B-Field
Palm
Direction of Forcemagnetic
Right Hand Rule
Fmagnetic
B
I
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What is the direction of Fmag?
SN
B
F ?
F
B ?
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What will the loop do?
N
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Magnitude of the Force
lIBkF
BF
IF
lF
lIBF
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Calculating the Force
lIBkF
sin lIBkF
Where θ is the angle between
the B-field and the current.
vector x vector = vectorDot Product
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)(TteslaaiswhichmA
NinB
Units of Magnetic Field
Thus k has a value of 1
if one uses these units.
sin
lI
FB
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Demonstration
Force on Parallel Current Carrying Wires
1. Current in same direction
Power Source, 2 swinging wires, support
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Demonstration
Force on Parallel Current Carrying Wires
2. Current in opposite direction
Power Source, 2 swinging wires, support
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Investigation
Force on a moving charge
Power source, magnet, cathode ray tube
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Force of a Charge in B-Field
t
qnI
t
lv
tvl
sin lIBF
sin
tvt
qnBF
)sin( vqBnF
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Force of a Charge in B-Field
)sin( vqBnF
sinvqBF
vqBF
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18.5Application
OfMagnetic Forces
OnConductors
694
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Moving-Coil Loudspeaker
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The Electric Motor
Demo
The Electric Motor
Green Power Sources – demo motor
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Build Electric Motor
Battery – Foam Cup – Coil Wire – Support Wire – Masking Tape
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18.7
The Mass of theElectronand theProton
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18.8
The Oscilloscope
708
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The Oscilloscope
Demonstration
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18.9
Mass Spectrograph
711
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18.10
ElectromagneticWaves
713
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18.11
Application ofElectromagnetic
Waves
718
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Seeing Soundon computer screen
Demonstration
Queue Sound Apparatus – Apple Computer – Tuning Fork
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Modulation of Sound on a Laser Beam
Demonstration
Laser – Radio – Solar Cell and Receiver
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That’s all folks!