Magnetic Fields and Electromagnetism

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Magnetic FieldsandElectromagnetism

• Created for CVCA Physics
• By
• Dick Heckathorn
• 19 April 2K4

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18.1 Natural Magnetism 676

• Investigation
• How Do Magnetic Regions
• Relate To Each Other?

Magnets
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What is the interaction force?
Repulsive
Repulsive
Attractive
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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?

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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

• Tie a paper clip to a string. Then move the arrow
  above the large magnet.
• Which way does the field really point?

Large Magnet - Arrow
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Investigate

• Place a magnet on a piece of paper.
• 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 end
• of compass points)

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A Question
Equally huge Newtons 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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Induced Magnetism

• Investigation
• Magnetizing a Needle
• or
• a piece of
• metal coat hanger

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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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Question

• How can one predict the direction of
• the magnetic field?
• Grab wire with thumb in direction of current,
  fingers give direction of field.

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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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Demonstration

• Put a ferromagnetic material in core of solenoid.

Power Source iron bolt - coil
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Permeability of Core Material

• is the magnitude of the
• magnetic field with core
• magnetic field without the core

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18.3 Application of Electromagnetism 684

• See text

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18.4 Magnetic ForcesonConductorsandMoving
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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Right Hand Rule
B

• Thumb
• Direction of Current
• Fingers
• Direction of B-Field
• Palm
• Direction of Forcemagnetic

Fmagnetic
I
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What is the direction of Fmag?
F
S
N
B
F ?
B ?
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Force is?
I
B
I
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Force is?
I
B
-

I
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What will the loop do?
N
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Magnitude of the Force
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Calculating the Force
vector x vector vector Dot Product
Where ? is the angle between the B-field and the
current.
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Units of Magnetic Field

• Thus k has a value of 1
• if one uses these units.

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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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(No Transcript)
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Investigation

• Force on a moving charge
• Power source, magnet, cathode ray tube

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(No Transcript)
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Force of a Charge in B-Field
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Force of a Charge in B-Field
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18.5 Application Of Magnetic Forces On Conductors
694
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Moving-Coil Loudspeaker
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Moving- Coil Galvanometer
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(No Transcript)
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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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18.6 Amperes Law 699
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In A Long Straight Wire
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In A Solenoid
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18.7 The Mass of the Electron and the Proton
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18.8 The Oscilloscope 708
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Demonstration
The Oscilloscope
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18.9 Mass Spectrograph 711
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18.10 Electromagnetic Waves 713
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(No Transcript)
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18.11 Application of Electromagnetic Waves 718
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Demonstration
Seeing Sound on computer screen
Queue Sound Apparatus Apple Computer Tuning
Fork
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Demonstration
Modulation of Sound on a Laser Beam
Laser Radio Solar Cell and Receiver
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Thats all folks!