Upload
lajos
View
37
Download
4
Embed Size (px)
DESCRIPTION
Announcements 11/16/12. Prayer Labs 8, 9 due tomorrow anyone still have issues with interferometer? Lab 10 due Tuesday Exam 3 starts Monday after break Exam 3 review session: Mon after break 4:30-6 pm, room ??? (I’ll tell you on Monday). Dilbert. From warmup (last time & this time). - PowerPoint PPT Presentation
Citation preview
Announcements 11/16/12 Prayer Labs 8, 9 due tomorrow
anyone still have issues with interferometer? Lab 10 due Tuesday Exam 3 starts Monday after break Exam 3 review session: Mon after break 4:30-6 pm,
room ??? (I’ll tell you on Monday)
Dilbert
From warmup (last time & this time)
Extra time on?a. Holograms (2 students)b. Yes, I don't understand how there is light in
the middle of the shadow of a penny in the example the book gave, does the penny have a small hole in the middle of it?– “Poisson spot”, aka “Arago spot”,
predicted by Fresnel in 1818
Other comments?a. You know what would be just really great?
Honors credit! I'm sure it's impossible at this point, but don't you think a harder class deserves more credit?
b. At the review session, can you give us a review of all things having to do with slits, equipping us with tools with which we can solve any slit problem that comes our way?
c. What is the best preparation for the final?
Clicker question:
What does Rayleigh’s criterion tell us?a. The angle at which both light
polarizations have equal reflection coefficients
b. The angle at which p-polarized light has minimum reflection
c. The angular separation resolvable by an imaging system
d. The number of orders produced by a diffraction grating
Suppose you are trying to resolve a binary star system with a telescope. Can you improve the resolving power (increase the resolution) using a color filter? Explain.
a. Wrong answers: index of refraction of air, anything to do with atmosphere, interference between colors, etc.
b. Right answer: Since a color-filter only lets in light of its color, or wavelength, it would be best to find a color filter that allows the lowest wavelength through, therefore lowering theta_min.
From warmup
min.resolve 1.22D
Circular Aperture, again
What do you get in this situation?
What if there’s a lens in the hole?
What if there isn’t a board?
What if you have two light sources?
patt
ern
at in
finity
patt
ern
at f
ocus
supe
rimpo
sed
patt
erns
at
focu
s
f
board with hole
Rayleigh: 2nd peak at position of first minimum
Rayleigh Criterion
plotted vs (D/)
Mathematica “FindRoot” command: D/ = 1.21967…
min.resolve 1.22D
(using sin )
Shape of curve involves a “Bessel
function”
Rayleigh Criterion
Cat's eyes have pupils that can be modeled as vertical slits. At night would cats be more successful resolving the headlights of a far away car if the car is horizontal (regular) or tilted vertically? Explain.
a. Vertically because then D would be greater and so the minimum angle would be smaller.
b. The cat would be better at resolving it if the car was tilted vertically. However, it would be worse for the car.
From warmup
3 slits, equally spaced
Back to 1-D slits, infinitely narrow
(created with parameters so period = 2)
4 slits, equally spaced
Back to 1-D slits, infinitely narrow
5 slits, equally spaced
Back to 1-D slits, infinitely narrow
10 slits, equally spaced
Back to 1-D slits, infinitely narrow
20 slits, equally spaced
Back to 1-D slits, infinitely narrow
100 slits, equally spaced
Back to 1-D slits, infinitely narrow
What have we learned?
The Grating Equation
Where will maxima be?
Resolving PowerN=100
0 .4 0 .2 0 .0 0 .2 0 .4
20
40
60
80
100
120
140
Goes to zero at x=0.0628
= 2/100
width = 1/N separation of
maxima
Resolving Power
Red light vs. Green light
HW 35-6(c): resolving power = / = Nm
Demos
Circular aperture Diffraction grating … with two lasers … with white light source
Clicker question:
Diffraction of x-rays off of planes of atoms in a crystal is governed by whose law?
a. Bragg’s Lawb. Bohr’s Lawc. Compton’s Lawd. Raman’s Lawe. Thompson’s Law
X-ray Diffraction by Crystals Bragg
equation
http://commons.wikimedia.org/wiki/File:Bragg_diffraction.png
http://l-esperimento-piu-bello-della-fisica.bo.imm.cnr.it/english/history/figuredett2.html
2dsin = m (constructive)
Laue Patterns
http://www.neutronoptics.com/laue.html