Announcements 3/25/11

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Announcements 3/25/11  Prayer  One lab due Saturday, two new labs start on Saturday.  We are nearing the homestretch for Optics… just two lectures…
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Announcements 3/25/11  Prayer  One lab due Saturday, two new labs start on Saturday.  We are nearing the homestretch for Optics… just two lectures after today. (After that, relativity!)  Exam 3 starts a week from tomorrow a. Review session next Thurs or Friday. I sent survey link. I will schedule the room on Monday morning, so please select your favorite times before then. Reading Quiz  Which of the following can generate a diffraction or interference pattern? a. Light passing through a pinhole in a card b. Light passing through an array of regularly spaced pinholes c. Light clipped by the edge of a razor blade d. Both A and B e. All of the above Review: Interference from slits  Quick writing: Using no equations, and in hopefully no more than two sentences, please explain how to solve slit problems. A “wide” slit (book: “narrow” slits)  HW 34-3. How do we solve this? “a” = width of slit 2    a sin   sin  x  Result: I ( )  I 0 sinc   New function: sinc(x)      x y  sin  x   approx.2: sin   What is lim   L x0 x   The sinc function sinc(x) [sinc(x)]2 1.0 1.0 0.8 0.8 Image credit: http://scripts.mit.edu/~tsg/ 0.6 0.6 www/list.php?letter=Q 0.4 0.4 0.2 0.2 15 10 5 5 10 15 0.2 15 10 5 0 5 10 15 Single slit max/min 15 10 2    a sin    I ( )  I 0 sinc  5      0 1.0 0.8 0.6 0.4 0.2 5 10 15  Under what conditions will you get a max?  Under what conditions will you get a min? What you need to know 2   a sin   2   ay  I ( )  I 0sinc   I ( )  I 0sinc       L   What sincx and sinc2x look like  The two formulas above (on notecard, unless you can quickly derive them)  How to do the integral (HW 34-3)  Conditions for max/min (on notecard, unless you can quickly derive them) Thought Question  I shine light through two tiny slits spaced by d. Then I shine the same light through a single slit with width d. Which diffraction pattern has the broadest middle peak? a. The two slit pattern b. The single slit pattern c. Both middle peaks are the same size. d. Masspacity  Not the answer!! λ=5a Image credit: Single slit diffraction pictures from Dr. Durfee λ=a λ = a/2 λ = a/3 λ = a/5 λ = a/10 Demo  Diffraction from a slit  Diffraction from a hair (Babinet’s principle, HW 34-2) Reading Quiz  When you have two slits close to each other, each slit being “wide” (at least, not infinitely narrow), the intensity you get on the screen is: a. A double-slit pattern b. A “wide” single-slit pattern c. A double-slit pattern PLUS a single-slit pattern d. A double-slit pattern TIMES a single-slit pattern Combination of patterns mins max max?  HW 34-4 1.0 0.8 0.6 0.4 0.2 1.5 1.0 0.5 0.0 0.5 1.0 1.5 2-D patterns  Pattern from x-direction  Pattern from y-direction Example: rectangular aperture zoomed in x y  Thought question: Which dimension of the rectangle was the narrowest? a. X b. Y Circular Aperture (more on this next time) Rectangle & Circle, side-by-side Array of Circles Thought Question I shine light through a piece of foil which has two identical holes shaped like tiny llamas spaced apart by a distance d. What will the diffraction pattern look like? A : The same as two narrow slits separated by d. B : The same produced by a single slit of width d. C : The diffraction pattern of a single llama. D : The diffraction pattern of a single llama multiplied by the two-slit pattern. E : none of the above Credit: All llama slides are from Dr. Durfee
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