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Reflection, Refraction, and Wave-Particles

This guide explores the fundamental concepts of light, including reflection, refraction, and its dual nature as both a wave and a particle. Light travels in transverse waves and can be polarized, impacting how it interacts with various surfaces. Learn about key phenomena like diffuse and regular reflection, the speed of light in different media, Snell's Law, and total internal reflection. Additionally, discover how temperature affects light speed, resulting in phenomena such as mirages. Delve into the photoelectric effect and the implications of wave-particle duality in the realm of modern physics.

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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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