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Announcements 11/16/12

Important announcements: prayer, labs 8 and 9 due tomorrow. Any issues with interferometer? Lab 10 due Tuesday. Exam 3 starts Monday after break. Review session on Monday for Exam 3. Additional topics discussed. Clicker question and relevant demonstrations.

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Announcements 11/16/12

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  1. 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

  2. From warmup (last time & this time) Extra time on? Holograms (2 students) 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? 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? 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? What is the best preparation for the final?

  3. Clicker question: • What does Rayleigh’s criterion tell us? • The angle at which both light polarizations have equal reflection coefficients • The angle at which p-polarized light has minimum reflection • The angular separation resolvable by an imaging system • The number of orders produced by a diffraction grating

  4. 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. Wrong answers: index of refraction of air, anything to do with atmosphere, interference between colors, etc. 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

  5. Circular Aperture, again

  6. What do you get in this situation? board with hole • What if there’s a lens in the hole? • What if there isn’t a board? • What if you have two light sources? superimposed patterns at focus pattern at infinity pattern at focus f

  7. Rayleigh: 2nd peak at position of first minimum

  8. Rayleigh Criterion Shape of curve involves a “Bessel function” plotted vs (qD/l) (using sinq q) Mathematica “FindRoot” command: qD/l = 1.21967… Rayleigh Criterion

  9. 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. Vertically because then D would be greater and so the minimum angle would be smaller. The cat would be better at resolving it if the car was tilted vertically. However, it would be worse for the car. From warmup

  10. Back to 1-D slits, infinitely narrow • 3 slits, equally spaced (created with parameters so period = 2p)

  11. Back to 1-D slits, infinitely narrow • 4 slits, equally spaced

  12. Back to 1-D slits, infinitely narrow • 5 slits, equally spaced

  13. Back to 1-D slits, infinitely narrow • 10 slits, equally spaced

  14. Back to 1-D slits, infinitely narrow • 20 slits, equally spaced

  15. Back to 1-D slits, infinitely narrow • 100 slits, equally spaced What have we learned?

  16. The Grating Equation • Where will maxima be?

  17. Resolving Power N=100 Goes to zero at x=0.0628 = 2p/100 width = 1/N  separation of maxima

  18. Resolving Power Red light vs. Green light HW 35-6(c): resolving power = l/Dl = Nm

  19. Demos • Circular aperture • Diffraction grating • … with two lasers • … with white light source

  20. Clicker question: • Diffraction of x-rays off of planes of atoms in a crystal is governed by whose law? • Bragg’s Law • Bohr’s Law • Compton’s Law • Raman’s Law • Thompson’s Law

  21. X-ray Diffraction by Crystals • Bragg equation 2dsinq = ml (constructive) http://commons.wikimedia.org/wiki/File:Bragg_diffraction.png http://l-esperimento-piu-bello-della-fisica.bo.imm.cnr.it/english/history/figuredett2.html

  22. Laue Patterns http://www.neutronoptics.com/laue.html

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