# Magnetic Fields and Electromagnetism

Document Sample

```					 Magnetic Fields
and
Electromagnetism
Created for CVCA Physics
By
Dick Heckathorn
19 April 2K+4

1
18.1 Natural Magnetism 676
Investigation

How Do Magnetic Regions
Relate To Each Other?

Magnets            2
What is the interaction force?

Repulsive

Repulsive

Attractive              3
Magnetic Fields
What is a magnetic field?

What is the symbol for magnetic
field?

B
What is its usefulness?

How do we see a magnetic field?
4
Investigation

Viewing a magnetic field

Magnets – spheres in Plexiglas   5
Magnetic Field Around a Bar Magnet

6
The Magnetic Field Between
Unlike Poles

7
The Magnetic Field Between
Like Poles

8
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    9
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   10
Investigate
3. Create the following.

11
Investigate
4. Would this be the end result if
one mapped the whole area?

12
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)
13
A Question

Equally huge – Newton’s 3rd Law   14
A problem

15
Demonstration

Which end of a magnet
points north?

2 Bar magnets – magnet holders - support   16
17
Question
How does the
earths magnetic north pole
compare to the
earth geographic north pole?

Handout: Magnetic Declination

2 Bar magnets – magnet holders - support   18
19
Magnetic
Declination
20
Demonatration

Breaking a magnet

Special magnets – compass - overhead   22
23
Investigation

Magnetizing
a temporary magnet
using a nail
and
DC current.

Battery – nail – wire – paper clips   24
18.2 Electromagnetism 681
What did Oersted discover?

Moving electric charges produce
a magnetic field.

25
Investigation

What exists around a current
carrying wire?

How is its direction defined?

Power Source – coils of wire - compasses   26
27
What one would see with a
magnetic field viewer.

28
Question

How can one predict the
direction of
the magnetic field?

Grab wire with thumb in
direction of current, fingers
give direction of field.     29
30
Thumb?
Direction of current.

Fingers?
Direction of magnetic field.

31
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   32
33
Question

What is the direction of the
magnetic field of a coil that has
a current in it?

34
35
36
Demonstration

Bring compass
near each end
of a coil.

37
How is the magnetic field of a
coil related to a magnet?

Like a bar magnet

But can be turned on and off

38
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   39
18.4 Magnetic Forces
on
Conductors
and
Moving Charges
page 687

43
Demonstration

Force on
current carrying wire
in a
magnetic field

Green power source, large magnet, swinging wire, support   44
Right Hand Rule
Thumb                        B
Direction of Current

Fingers
Direction of B-Field

Palm                  Fmagnetic        I
Direction of Forcemagnetic
45
What is the direction of Fmag?
F
S
N
B
F?
B?

46
48
50
What will the loop do?

N

51
Magnitude of the Force
    
F B F I F l
      
F  B  I l
      
F  k B  I l
52
Calculating the Force
       
F  k B  I l
vector x vector = vector
Dot Product

F  k  B  I  l  sin
Where θ is the angle between
the B-field and the current.   53
Units of Magnetic Field
          F
B
I  l  sin
     N
B in      which is a tesla (T )
A m
Thus k has a value of 1
if one uses these units.   54
Demonstration

Force on Parallel
Current Carrying Wires

1. Current in same direction

Power Source, 2 swinging wires, support   55
56
Demonstration

Force on Parallel
Current Carrying Wires

2. Current in opposite direction

Power Source, 2 swinging wires, support   57
58
Investigation

Force on a moving charge

Power source, magnet, cathode ray tube

59
60
Force of a Charge in B-Field
n q         l
I         v             l  v  t
t         t

F  B  I  l  sin
       nq
F B          v  t  sin
t

F  n( B  q  v sin )             61
Force of a Charge in B-Field

F  n( B  q  v sin )

F  B  q  v sin
       
F  B qv              62
18.5
Application
Of
Magnetic Forces
On
Conductors
694
63
Moving-Coil
Loudspeaker

64
66
The Electric Motor
Demo

The Electric Motor

Green Power Sources – demo motor   67
Build Electric Motor

Battery – Foam Cup – Coil Wire – Support Wire – Masking Tape   68
18.7

The Mass of the
Electron
and the
Proton

72
18.8

The Oscilloscope

708

73
Demonstration

The Oscilloscope

74
18.9

Mass Spectrograph

711

75
18.10

Electromagnetic
Waves

713

76
77
18.11

Application of
Electromagnetic
Waves

718
78
Demonstration

Seeing Sound
on computer screen

Queue Sound Apparatus – Apple Computer – Tuning Fork   79
Demonstration

Modulation of Sound
on a Laser Beam

That’s all folks!

81

```
DOCUMENT INFO
Shared By:
Categories:
Stats:
 views: 15 posted: 9/23/2010 language: English pages: 71