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# Notes on Optics

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DES Notes on Optics

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### Notes on Optics

1. 1. Optics -- How We See Space<br />
2. 2. What are “Optics?”<br />For this class we are going to define “optics” as the study of light and how it interacts with the mirrors and lenses that let us see into space.<br />
3. 3. Our Study Starts with Light<br />Light basically moves in straight lines.<br />An object “lights up” either because it is actually emitting light, or light is being reflectedoff its surface.<br />
4. 4. When Light Hitsa Surface…<br /> It can be REFLECTED<br />Light bouncesbackat the same angle it hits a surface.<br />
5. 5. When Light Hitsa Surface…<br /> It can also be REFRACTED<br />Light “bends” in response to entering a different medium(i.e. from air to water or from air to glass)<br />
6. 6. Let’s Start by Studying Reflection<br />The Law of Reflection:<br />When a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflectionrelative to the normal.<br />
7. 7. The Law of Reflection<br />The normal is: always at a right angle to the surface being used.<br />
8. 8. SPECULAR reflection happens when lighthits and bouncesback off a SMOOTHsurface.<br />DIFFUSE reflection happens when lighthits and bouncesback off a ROUGHsurface.<br />
9. 9. Now Let’s Look at Mirrors<br />Plane mirrors = straight/flat mirrors<br />Spherical Mirrors = curved/rounded mirrors (convex or concave)<br /> *** For ALL mirrors, the angle of incidence equals the angle of reflection (relative to a 90 “normal” line). . <br />
10. 10. Plane or Straight Mirrors<br />Angle of incidence = angle of reflection.<br />A plane mirror “fools you” by making your eyes and brain perceive a virtual image. The image is called “virtual” because it’s not really there.<br />The image appears to be the same distance behind the mirror as the object is in front of the mirror.<br />
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12. 12. “Spherical” (Curved) Mirrors<br />For both curved mirrors, the angle of incidence equals the angle of reflection.<br />A convex mirror will always produce a virtualimage of an ordinary object.<br />A concave mirror can produce a virtual or a real image, depending on how close the object is to the mirror. <br />
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14. 14. Virtual vs. Real Image? <br />You have to look at a lens or mirror to see a virtual image<br />You can see a real image without actually seeing the lens or mirror that created it. <br />
15. 15. What is “Refraction?”<br />Refraction: Light refracts (bends) when it crosses a boundarybetween two differentmedia(air to water ; air to glass)<br />
16. 16. Law of Refraction<br />The Law of Refraction (Snell’s Law):<br />The degree to which light will bend depends on the indices of refraction of the media involved.<br />
17. 17. What is “Refraction?”<br />Light slows downwhen it enters a more densemedium.<br />Light speeds upwhen it enters a less dense medium.<br />
18. 18. The index of refraction tells us how much light slows downin different materials.<br />Dense materials have a high index of refraction & cause light to bend more. (glass, diamonds)<br />The Index of Refraction:<br />
19. 19. <ul><li>Light bends towards the normal in dense material (glass, water, diamond)
20. 20. Light bends away fromthe normal in less dense material (air)</li></ul>Remember that 90 degrees “Normal” Reference Line!<br />
21. 21. Take a Look at Lenses<br /> A lens is a specially-shaped piece of transparent material like glass or plastic used to bend light<br />Convex = converging lens (light comes together)<br />Concave = diverging lens (light spreads out)<br />