Almost There! Turn in Unit 16 for Grading Exam-3 Lab reports Told you about these last time Assorted small stuff Working very hard on this but am being careful. I stopped to put this presentation together but I might get it done. Or not. Will be reviewed when returned. All papers will be returned either Monday or at the final exam. All grades will have been updated. Clicker Grades Some time this week via posted file with messed up PIDs. Sunday Monday Tuesday Wednesday Thursday Friday Saturday 1 2 3 4 Complete Induction 5 6 AC 7 8 AC Quiz? 9 10 11 COMPLE TE AC EXPT 12 13 OPTICS 14 15 OPTICS 16 17 18 EXAM #3 (No Optics) 19 24 25 (LAST LASS) 26 OPTICS POST TEST EM Waves POLARIZATI ON Quiz 20 OPTICS 21 22 OPTICS 23 27 28 29 30 FINAL HPA 119 9:00 AM 4 Light travel’s at a speed c in a vacuum. In an actual material, it travels a bit slower, at a velocity of v. The speed of light depends on the material through which it is traveling. DEFINITION – INDEX OF REFRACTION (or refractive index): velocityof light in a vacuum n 1 velocityof light in a transparant medium 6 7 8 Notice c v v f n n For two materials c c 1 vacuum f f vacuum n1 1 vacuum n2 2 divide n1 2 n2 1 9 Huygen’s Principle Each point on a wavefront acts as a secondary source of spherical waves that progress from the source at the speed of light (whatever it may be). A spherical wave with very large radius, behaves as a plane wave. 10 Far, far away 11 . Not there yet! PHY102 12 The Wave Nature of Light The law of refraction is explained by Huygen’s Principle The little wavelets move slower in medium 2 than in medium 1. Doing the tangent shows how the wave fronts bend. 13 Some Geometry 900 900 14 The Wave Nature of Light sin 1 v1 c / n1 n2 sin 2 v2 c / n2 n1 n1 sin 1 n2 sin 2 2 v2t v2 c / n2 n1 1 v1t v1 c / n1 n2 ADC 2 BAD 1 v1t v2t sin 1 and sin 2 AD AD If medium 1 is air, then n1 1 and v1 c and 1 n /n 15 Snell’s Law of Refraction n1 sin 1 n2 sin 2 Law of Reflection 1 2 16 Both Together 17 18 nb na na Sin critical nb sin(900 ) nb nb Sin critical na At the critical angle and beyond, only reflection is possible. 19 Total Reflection – Optical Fiber 20 Waves on a string. 21 dichroism 80% 1% of opposite polarization 22 23 Let’s do some problems if we have sufficient time…. • No, this is NOT a test! • Follow the instructions on first page. • Do the other problems at home.