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Lecture 35: WED 15 APR Ch:33.8-10

Physics 2102 Jonathan Dowling. Lecture 35: WED 15 APR Ch:33.8-10. Reflection and Refraction. When light finds a surface separating two media (air and water, for example), a beam gets reflected (bounces) and another gets refracted (bends).

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Lecture 35: WED 15 APR Ch:33.8-10

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  1. Physics 2102 Jonathan Dowling Lecture 35: WED 15 APR Ch:33.8-10

  2. Reflection and Refraction When light finds a surface separating two media (air and water, for example), a beam gets reflected (bounces) and another gets refracted (bends). Law of reflection (Light Bounces): the angle of incidence 1 equals the angle of reflection ’1. 1 = ’1 n is the index of refraction of the medium. In vacuum, n = 1. In air, n ~ 1. In all other media, n > 1.

  3. Hits Sand Turns Left Road vL vR Speed of Light is Slowed n>1 Plastic Glass n=1 n>1

  4. Example Water has n=1.33. How much does a beam incident at 45o refracts? n2 sin q2= n1 sin q1 sin q2= (n1 /n2) sin q1 =(1/1.33) sin 45o =0.0098 q2= 32o

  5. Water on Desert Road Illusion The index of refraction decreases with temperature: the light gets refracted and ends up bending upwards. We seem to see water on the road, but in fact we are looking at the sky!

  6. Water on the Desert Road Mirage

  7. Chromatic Dispersion The index of refraction depends on the wavelength (color) of the light. Rainbow!

  8. The Single Rainbow

  9. The Double Rainbow Total Internal Reflection!

  10. Total Internal Reflection From glass to air, the law of refraction uses n2<n1, so 2> 1: it may reach 90o or more: the ray is “reflected” instead of “refracted”. 2 n2~1 Condition for TIR: n2 sin2= n1 sin1 & ≥  1 n1>1 For glass (fused quartz) n=1.46, and the critical angle is 43o: optical fibers!

  11. Total In Turtle Reflection!

  12. The cut of the diamond favors total internal reflection. Most rays entering the top of the diamond will internally reflect until they reach the top face of the diamond where they exit. This gives diamonds their bright sparkle. A fiber optic is a glass "hair" which is so thin that once light enters one end, it can never strike the inside walls at less than the critical angle. The light undergoes total internal reflection each time it strikes the wall. Fiber optic cables are used to carry telephone and computer communications.

  13. Fiber Optic Cables

  14. FIBER OPTIC GUIDED MISSILE

  15. Polarization By Reflection Different polarization of light get reflected and refracted with different amplitudes (“birefringence”). At one particular angle, the parallel polarization is NOT reflected at all! This is the “Brewster angle” B, and B + r = 90o. Polarizing Sunglasses

  16. Polarized Sunglasses

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