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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!