The Electric Vector in Light Waves
Polarization of Light Waves
Exam 2 Statistics
Exam 2
Ave=16
5
Exam 1
Ave = 15
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4
Y Axis Title
Y Axis Title
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1
1
0
0
7
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16
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21
7
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X Axis Title
10
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X Axis Title
Each atom produces a
wave with its own
r
orientation of E
All directions of the
electric field vector are
equally possible and
lie in a plane
perpendicular to the
direction of
propagation
This is an unpolarized wave
Liquid Crystal Displays (LCDs)
One use of polarized Light
Polarized Light
A wave is said to be linearly
polarized if the resultant
electric field vibrates in the
same direction at all times at
a particular point
It may vibrate in any fixed
direction
Quiz
Polarization can be obtained from an unpolarized
beam by
A. selective absorption
B. reflection
C. Scattering
D. All of the above
E. None of the above
The molecules of the substance are more orderly than
those of a liquid but less than those in a pure crystalline
solid
In a display, the liquid crystal is placed between two
glass plates with electrical contacts
A voltage is applied across any segment in the display and that
segment turns on
V=0 rotates Polarization 90° making it Bright
Light passes through the polarizer on the right
and is reflected back to the observer, who sees
the segment as being bright
A liquid crystal is intermediate between a
crystalline solid and a liquid
V≠0 produces no rotation making it Dark
The light is absorbed by the polarizer on the right and
none is reflected back to the observer
Magnetism-Magnetic Fields
Poles of a magnet are the ends where objects
are most strongly attracted
Two poles, called north and south
Like poles repel each other and unlike poles
attract each other
Similar to electric charges
Magnetic poles cannot be isolated
If a permanent magnetic is cut in half
repeatedly, you will still have a north and a
south pole
This differs from electric charges
There is some theoretical basis for
monopoles, but none have been detected
Sources of Magnetic Fields
The region of space surrounding a
moving charge includes a magnetic field
The charge will also be surrounded by
an electric field
A magnetic field surrounds a properly
magnetized magnetic material
Soft magnetic materials, such as iron, are
easily magnetized
They also tend to lose their magnetism
easily
Hard magnetic materials, such as cobalt and
nickel, are difficult to magnetize
They tend to retain their magnetism
Magnetic
Fields
r
Symbolized by B
Direction is given by the direction a north pole
of a compass needle points in that location
Magnetic field lines can be used to show how
the field lines, as traced out by a compass,
would look
Earth’s Magnetic Field
The Earth’s geographic north pole corresponds
to a magnetic south pole
The Earth’s geographic south pole corresponds
to a magnetic north pole
Strictly speaking, a north pole should be a
“north-seeking” pole and a south pole a
“south-seeking” pole
Quick Quiz
The red end of a compass needle which points
“North” is which end of a dipole magnet?
Electric Charges in Magnetic Fields
Moving charges feel magnetic force
perpendicular to path of
This force has a maximum value when
the charge moves perpendicularly to the
magnetic field lines
This force is zero when the charge moves
along the field lines
This force is zero if the charge is stationary
F = Bqv sin θ
Superconducting magnets
300000 Gauss or 30 Tesla
Earth’s magnetic field
-5 T
0.5 G or 5 x 10
Quick Quiz
How many G in a T?
D. 105
A.10-5
E. 0.5 x 10-5
B.10-4
C.104
A. North pole
B. South pole
Right Hand Rule
Place your fingers
in the
r
direction of v
Curl the fingers in the
direction
r of the magnetic
field, B
Your thumb points in the
r
direction of the force,F , on a
positive charge
If the charge is negative, the
force is opposite that determined
by the right hand rule