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Reflection, Refraction, and Wave-Particles

Reflection, Refraction, and Wave-Particles. Reminders. Light travels in transverse waves Waves can be oriented to be: Up and down Left and right Any combination. What is polarized?. LCDs like that of your calculator are polarized

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Reflection, Refraction, and Wave-Particles

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  1. Reflection, Refraction, and Wave-Particles

  2. Reminders • Light travels in transverse waves • Waves can be oriented to be: • Up and down • Left and right • Any combination

  3. What is polarized? • LCDs like that of your calculator are polarized • When light is reflected off a surface, it is polarized (check it out!)

  4. On to Reflection • When light is reflected, it can be done so in two ways • Diffuse Reflection • Light is reflected in many different ways when shone on a rough surface • Regular Reflection • Light follows the law of reflection when it is shone on a smooth surface

  5. Law of Reflection • Definition: the angle of incidence from the normal equals the angle of reflection from the normal

  6. The Speed of Light • In a vacuum, light travels at 3.0*108 m/s (forever now denoted as c) • However, in media that is more dense (ex: water), light travels slower • Aquarium examples

  7. More Refraction • Refracted light follows Snell’s Law • n stands for the index of refraction • Each media has its own index, with more dense media having higher indices

  8. Refraction shown Graphically • Which material is more dense? • How can you tell? • Try it on your calculator • A few indices • Water = 1.33 • Glass = 1.5 • Diamond = 2.42

  9. Archer Fishes • Archer Fish shoot a stream of water • Water knocks the bug down

  10. Ahhh!!! Refraction! • Fishing story

  11. How do we come up with these indexes, indices, or whatever? • Each index is equal to the ratio of the speed of light in a vacuum to that in the material • ns is the index and vs is the speed of light in the substance

  12. Total Internal Reflection • When light passes from a substance with a higher index of refraction (more dense) to a lower one, it can be totally reflected • If the light is reflected, it follows the law of reflection

  13. More total internal reflection • For total reflection to occur, the following must happen: • In this occasion, the angle is then • n1 is the more dense substance

  14. Refraction and Mirages • In air, light also travels at different speeds • In hot air, light travels faster • In cold air, light travels slower • Because of this phenomena, mirages can form

  15. Mirage • A mirage is a refraction phenomena that happens when an object appears in a different place than it actually exists

  16. Here’s what’s going on…

  17. Whiteboard Practice • Ready • Set • Go get ‘em!

  18. If light is shown on a smooth surface, what is the angle of reflection if: • The angle of incidence from the normal is 32o • The angle of incidence from the surface is 32o

  19. Light is incident in air (n=1) upon a piece of glass (n = 1.5) at a 45 angle. • What is the speed of light in glass? • What is the angle of refraction?

  20. Looking at the bottom of a pool you look up at a 35 angle from the normal • What is the speed of light in water (n = 1.33)? • What angle from the water (not the normal!) do you see items outside?

  21. What is the angle for total internal reflection: • From water (n=1.33) to air (n=1)? • From glass (n=1.5) to air? • From glass to water? • From air to glass?

  22. Is light a particle or a wave?

  23. Well… • It’s a wave because it can be polarized • It’s a wave because when you pass monochromatic light through a slit, it diffracts.

  24. So…Why is it a particle? • The photo-electric effect • High energy photons were shot at a metallic sheet and electrons shot off • Without this property of waves, you can forget about photo-voltaic cells! (or just solar-powered stuff)

  25. Let’s get a little twisted…and maybe your head will smoke like mine used to… • Einstein found that E=mc2 according to special relativity • Then deBroglie found that wavelength of a photon is equal to h/p where p is the momentum • But there’s no mass….soooo….uhh…

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