# AB rief History of Planetary Science

Document Sample

```					     Electromagnetic Waves

Physics 202
Professor Vogel
(Professor Carkner’s
notes, ed)
Lecture 11
Polarization
 An EM wave has both an
electric and magnetic
component
 The plane containing the E
vectors is called the plane
of oscillation
 EM waves in which the E
vector are preferentially
located in specific planes
are polarized
 Most light sources are
unpolarized
 Any given wave has a
random plane of oscillation
Polaroid
 We can polarize unpolarized
light by passing it through a
sheet of Polaroid
 Polaroid is a sheet of material
that will only pass through
the components of the E
vectors in a certain direction
 Example: if you pass
unpolarized light through a
vertical sheet of Polaroid, it will
become vertically polarized
 If you put a horizontal
Polaroid sheet on top of a
vertical Polaroid sheet no
light gets through
Polarization and Intensity
You can resolve unpolarized light into its
components on the y-z plane
The sum of all of the y components should be
equal to the sum of all of the z components
If you polarize the light along one direction
you remove half of the intensity:
I = ½ I0
This is true only when the incident light is
completed unpolarized
What about polarized light hitting Polaroid?
Incident Polarized Light
 For polarized light incident on a
sheet of Polaroid, the resultant
intensity depends on the angle q
between the original direction of
polarization and the sheet
 The new electric field becomes:
E = E0 cos q
 Since I depends on E2 it becomes:
I = I0 cos2 q
 This is only true for polarized light
 For unpolarized light that pass
through two polarizing sheets, q
is the angle between the two
sheets
Multiple Sheets
Sheet Angles
Means of Polarization
A sheet of Polaroid has long molecules embedded
in it all aligned in one direction
This alignment permits only the components
perpendicular to that direction to pass
A similar effect is seen in light passing through
interstellar dust clouds
The dust grains are partially aligned by the galactic
magnetic field and so the light is partially polarized
Light can also be polarized by reflection
Polarization By Reflection
 Light reflected off of a
surface is generally
polarized
 This is why polarized
sunglasses reduce glare
 When unpolarized light
hits a horizontal surface
the reflected light is
partially polarized in
the horizontal direction
and the refracted light
is partially polarized in
the vertical direction
Brewster Angle
At a certain angle, known as the Brewster angle, the
reflected light is totally polarized
At qB the reflected and refracted rays are
perpendicular to each other, so
qB + qr = 90
Since n1 sin qB = n2 sin qr we get
qB = tan-1 (n2/n1)
If we start out in air n1 = 1 so:
qB = tan-1 n
This is Brewster’s Law

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 0 posted: 9/29/2012 language: Unknown pages: 10
How are you planning on using Docstoc?