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# Announcements 10/26/11

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 Covers through tonight’s HW (HW 24) Like last time, no notes allowed, but I give you equations

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## Announcements 10/26/11

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1. 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 • Covers through tonight’s HW (HW 24) • 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

2. Reading Quiz • Which of the following scientists did not attempt to make a measurement of the speed of light? • Einstein • Fizeau • Galileo • Roemer • 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

4. The wave nature of light • What is “waving”? http://stokes.byu.edu/emwave_flash.html • Medium? • Polarization: quick definition

5. 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.) • When λ << d • When λ ≈ d • When λ >> d

6. Next three slides: image credit to Dr. Durfee

7. Index of Refraction v = c/n • Book table

8. Index of Refraction Different wavelengths have different speeds! Song: Roy G. Biv (start at 0:30) http://www.youtube.com/watch?v=Gf33ueRXMzQ v = lf linside = lvacuum/n Different wave-lengths (k values) have different speeds! (l going into material) Dispersion! blue green red Image: http://en.wikipedia.org/wiki/Dispersion_(optics)

9. Thought question • Which color of light travels fastest in glass? • Red • Green • Blue • Same

10. Absorption • “Lorentz oscillator model” “anomalous” index of refraction index of refraction absorption increasing frequency (decreasing l) From Peatross & Ware, textbook for Phys 471 Why is blue light slower through glass than red light?  It’s closer to an absorption region

11. fast light (smaller n) q1 slow light (larger n) q2 Index of Refraction • Light ray at boundary

12. fast light (smaller n) q1 slow light (larger n) q2 Snell’s Law • n1sinq1 = n2sinq2 Advertisement for Phys 442/471

13. Law of Reflection • qrefl. = q1 fast light (smaller n) q1 qrefl. Reflections occur off of any boundary, not just “mirrors” slow light (larger n) q2 When will you have no reflection?

14. Fresnel Coefficients / Fresnel Equations • If near perpendicular (1-D problem) Look familiar?? • For arbitrary angle (these eqns not needed for HW/exam) Advertisement for Phys 442, Phys 471

15. top bottom Thought question • 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? • top • bottom

16. Demos • Reflection/refraction using water-soluble oil • “Blackboard optics”

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