1 / 14

Announcements 11/11/11

Announcements 11/11/11. Prayer Lab 8 going on, due on Sat Nov 19 Lab 9 starts tomorrow, due on Sat Nov 19 Lab 10 starts tomorrow, due on Tues Nov 22 Slinky (down to you, Thomas…). Two facts you should know:. (They follow quickly from e ix = cosx + i sinx). Reading Quiz.

Download Presentation

Announcements 11/11/11

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 11/11/11 • Prayer • Lab 8 going on, due on Sat Nov 19 • Lab 9 starts tomorrow, due on Sat Nov 19 • Lab 10 starts tomorrow, due on Tues Nov 22 • Slinky (down to you, Thomas…) Two facts you should know: (They follow quickly from eix = cosx + i sinx)

  2. Reading Quiz • According to the book, a double-slit diffraction pattern (viewed on a screen far from the slits) is: • A series of equal amplitude peaks, equally spaced • A series of equal amplitude peaks, alternating between two spacing distances • A series of alternating amplitude peaks, equally spaced • A series of alternating amplitude peaks, alternating between two spacing distances

  3. Two slit interference From Wikipedia http://en.wikipedia.org/wiki/Double-slit_experiment

  4. intensity screen here Double slit experiment aka “Young’s Double Slit” • Exactly the same as the two speaker demo • Goal: what’s the shape of that curve? How can we predict where the maxima & minima will be? min max min max

  5. Wait, which is correct? Experimental challenge • How do you get two points sources of light that are oscillating in phase with each other? • How did we do it with sound? • Options for light? (I can only think of two) • What he did: http://en.wikipedia.org/wiki/ Young's_Double_Slit_Interferometer

  6. How to solve the problem • Complex numbers!! • The light from each slit travels a different distance • This creates a phase shift • Incorporate the phase shift into eif • First: what’s the phase shift for two waves oscillating in phase with a known DPL? f = ( DPL / l )  360 f = 2pDPL / l

  7. What’s DPL? f = 2pDPL / l • Clicker Vote: What should we measure the path length relative to? • The top slit • The bottom slit • Halfway between the two slits Approximation #1: d is small enough that the two rays are parallel. Requires d << L.

  8. The Easy Part • Maxima/minima Maxima: DPL = ? Minima: DPL = ?

  9. The Full Answer f = 2pDPL / l • Etot = Etop slit + Ebottom slit = [use whiteboard] • I ~ |E|2 I = [use whiteboard] • Plot of I(y) for I0=1, l=500 nm, L=1 m, d=1mm • How did I turn q into y? • Approximation #2: sometimes (not here!) q is small enough that q  y/L. Requires y << L.

  10. Plots (approx. 1 and 2) (approx. 1 only)

  11. intensity screen here min max min max

  12. max min max min max min max screen here

  13. Maxima/minima, revisited • Max: cosx = 1  … • Min: cosx = 0  …

  14. What you need to know Not given on exam Given on exam • HW 32-4: Solve the three slit problem • Exam problem likely (possibly extra credit) • Disclaimer: This only works for very narrow slits  Lecture after next: wide slits Demo: Double slit experiment!

More Related