1 / 15

Announcements 11/12/10

Announcements 11/12/10. Prayer Two labs this week (telescope, interferometer) The missing exams… Project progress reports: I’m about 75% of the way done Review:. Fourier Transforms?. From last time: what did our two-slit analysis have to do with Fourier transforms?.

lottie
Download Presentation

Announcements 11/12/10

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Announcements 11/12/10 • Prayer • Two labs this week (telescope, interferometer) • The missing exams… • Project progress reports: I’m about 75% of the way done • Review:

  2. Fourier Transforms? • From last time: what did our two-slit analysis have to do with Fourier transforms? (this is the y-coordinate on the slits, not the y-coordinate on the screen)

  3. Adding up phases • For an equally-spaced pattern of slits, how do the DPLs compare? • Each f is a multiple of f1! (Could have an overall reference phase…not too important.) In short, we need to add up a bunch of vectors that have the same magnitude (1), but angles (phases) that go like 0, 20, 40, 60, etc. … For a different position on the screen (measured by y or q, we need to add up a different set of phases… perhaps like 0, 21, 42, 63, etc. slits screen

  4. Adding up phases, cont. • Quick writing: graphically add these three vectors: 10 + 120 + 140 • What about 10 + 190 + 1180 … slits screen

  5. Three Slit Problem: Scanning Theta Credit: this animation and the next one are from Dr. Durfee Note: for some reason he picked the overall reference phase to be about 20

  6. Thought question • How many “sub” peaks are there between the “main” peaks in a 5-slit interference pattern? • 1 • 2 • 3 • 4 • 5

  7. Five Slit Problem: Scanning Theta Note: for some reason he picked the overall reference phase to be about 20-30

  8. Reading Quiz • How does the phase shift of a light wave switching between fast and slow media compare to the phase shift of a wave on a string switching between fast and slow media? • The phase shift is the same • The phase shift is the same for fast-to-slow, but reversed for slow-to-fast • The phase shift is the same for slow-to-fast, but reversed for fast-to-slow • The phase shift is reversed for both cases • What is the phase shift?  180

  9. Remember these? • “Fresnel Equations” Just the same as strings If near perpendicular (1-D problem) For arbitrary angle The Truth: if at an angle, you don’t always get a phase shift, even if going fast to slow. (Brewster) More Truth: sometimes phase shifts not just 180: complex n, complex q, etc. Too much info!!

  10. Rays drawn at an angle to make viewing easier. They’re really perpendicular to surface. Back to 1D case • From low to high index: 180 phase shift • From high to low index: no phase shift • Quick writing: What does the thickness of this slab need to be to get constructive interference between the two rays? What changes if rays really are at an angle? air thin glass thickness t air

  11. Optical path length • OPL = Path Length  n  since wavelength inside the material is reduced by a factor of n, the distance “looks” bigger than it actually is • Constructive interference: OPL ( any phase shifts) = ml • Destructive interference: OPL ( any phase shifts) = (m+1/2) l

  12. New situation • What does the thickness of the COATING need to be to get constructive interference between the two rays? Rays drawn at an angle to make viewing easier. They’re really perpendicular to surface. air thin coating, n = 1.3 thickness t thick glass, n = 1.5

  13. Pretty pictures • What’s going on here? http://twilit.wordpress.com/2008/03/15/bubbles-and-interference/ http://superphysics.netfirms.com/pp_optics.html

  14. Demo/Video • Video: glass plates in sodium light • Demo: Soap film

  15. Interferometer • From lab 9: changing optical path length, yields ngas Interference! How does this disprove the ether?

More Related