Announcements 10/26/11

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Announcements 10/26/11  Prayer  Slinkies: Please turn-in, and cross your name off of the sign out list.  Exam 2 starts tomorrow, goes through Tuesday…
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Announcements 10/26/11  Prayer  Slinkies: Please turn-in, and cross your name off of the sign out list.  Exam 2 starts tomorrow, goes through Tuesday evening a. Covers through tonight’s HW (HW 24) b. Like last time, no notes allowed, but I give you equations  Comment from Chris: when turning in multiple assignments, staple them separately.  Found a white sweater after review session last night. Overboard Reading Quiz  Which of the following scientists did not attempt to make a measurement of the speed of light? a. Einstein b. Fizeau c. Galileo d. Roemer e. Michelson (OK, this is not the answer, but I felt his name should be included on the list even though he wasn’t mentioned in today’s reading, because he performed the “canonical experiment”) How did they all attempt to measure it? Advertisement for Phys 471 xkcd Advertisement for Phys 222 The wave nature of light  What is “waving”? http://stokes.byu.edu/emwave_flash.html  Medium?  Polarization: quick definition Reading Quiz  A beam of light passes through a hole of diameter d in a metal plate. Under what condition are we allowed to ignore the diffraction or “spreading” of the light? (This is called the ray approximation.) a. When λ d b. When λ ≈ d c. When λ d lambda = d/10 50 100 150 200 250 300 350 400 450 500 50 100 150 200 250 300 350 400 450 500 Next three slides: image credit to Dr. Durfee lambda = d/4 50 100 150 200 250 300 350 400 450 500 50 100 150 200 250 300 350 400 450 500 lambda = d 50 100 150 200 250 300 350 400 450 500 50 100 150 200 250 300 350 400 450 500 Index of Refraction v = c/n  Book table Index of Refraction Different wavelengths have different speeds! v = lf linside = lvacuum/n Different wave- lengths (k values) have different speeds! (l going into material) Dispersion! blue green red Image: Song: Roy G. Biv (start at 0:30) http://en.wikipedia.org/wiki http://www.youtube.com/watch?v=Gf33ueRXMzQ /Dispersion_(optics) Thought question  Which color of light travels fastest in glass? a. Red b. Green c. Blue d. Same Absorption  “Lorentz oscillator model” “anomalous” index of refraction index of refraction absorption increasing From Peatross & Ware, frequency textbook for Phys 471 (decreasing l) Why is blue light slower through glass than red light?  It’s closer to an absorption region Index of Refraction  Light ray at boundary fast light q1 (smaller n) slow light q2 (larger n) Snell’s Law  n1sinq1 = n2sinq2 fast light q1 (smaller n) slow light q2 (larger n) Advertisement for Phys 442/471 Law of Reflection  qrefl. = q1 fast light q1 qrefl. Reflections occur (smaller n) off of any boundary, not just “mirrors” slow light q2 (larger n) When will you have no reflection? Fresnel Coefficients / Fresnel Equations  If near perpendicular (1-D problem) v2  v1 n1  n2 2v2 2n1 r  t  v1  v2 n1  n2 v1  v2 n1  n2 2 2 R r T  1 r Look familiar??  For arbitrary angle (these eqns not needed for HW/exam) n1 cosq1  n2 cosq2 2n1 cosq1 rs polar .  ts polar .  n1 cosq1  n2 cosq2 n1 cosq1  n2 cosq2 n1 cosq2  n2 cosq1 2n1 cosq1 rp polar.  t p polar.  n1 cosq2  n2 cosq1 n1 cosq2  n2 cosq1 Advertisement for Phys 442, Phys 471 Thought question top bottom  I send white light into a prism as shown below (n 1). Will the red part of the “rainbow” be on the top or the bottom of the outgoing fan of light? a. top b. bottom Demos  Reflection/refraction using water-soluble oil  “Blackboard optics”
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