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Announcements 10/28/11 Prayer Exam 2 going on… Slinkies: Please turn in and cross your name off the signout list Speed Bump Reading Quiz What is a “wave front”? a. The crest of the wave, repeated every l b. The complex phase of a wave c. The first part of the wave to reach an object d. The reflection of a wave off of a surface e. The students at the football game who start “The Wave” Law of reflection illustrated Credit: next several slides from Dr. Durfee Law of reflection illustrated Law of reflection illustrated Law of reflection illustrated Law of reflection illustrated Law of reflection illustrated Snell’s Law illustrated Snell’s Law illustrated Snell’s Law illustrated Reading Quiz What do we call the phenomena which makes fiber optics possible? a. Brewster’s Law b. Equivalence Theorem c. Fermat’s Principle d. Superluminal Energy Transport e. Total Internal Reflection Demo Stokes computer demo: (5:00) http://stokes.byu.edu/refract_script_flash.html Total Internal Reflection TIR: the equation Demos Blackboard optics TIR in water soluble oil Laser captured in stream of water Fiber Optics Thought question If you have a -0.3 dB change, the final intensity is what fraction of the initial intensity? (You’ll need your calculator.) a. 78% b. 83% c. 88% d. 93% e. 98% -0.3 dB 93.3% -0.2 dB 95.5% -0.1 dB 97.7% Reading Quiz When we think of all the points on a wave front as little sources of secondary waves in order to calculate what the wave front will look like after propagating some distance, we are using the idea known as... a. the Equivalence theorem b. Huygen’s Principle c. Fermat’s Principle d. Newton’s first law of optics e. the Wavelet theorem Huygen’s Principle Image credit: Wikipedia Each wavefront serves as source of spherical waves HW 26-5 (extra credit): a. “Stare at the picture until you can visualize that the green lines tangent to the circles connect matching wavefronts.” b. Construct an accurate picture like this for a specific situation, show graphically that it gives you Snell’s law Huygen’s Principle, cont. Image credit: Wikipedia http://en.wikipedia.org/wiki/ Double-slit_experiment A wave hits the two slits Each slit (infinitely narrow) becomes source of spherical waves The waves from those two sources interfere with each other Spherical Waves Credit: the next few slides are from Dr. Durfee Huygen’s Construction of a Spherical Wave Huygen’s Construction of a Plane Wave