Which is darker? A or B?

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Margery Stephens
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1 Optics

2 Circles or Spiral?

3 Which is darker? A or B?

9 Confused yet?

10 Everybody loves Ray diagrams! Ray Diagrams

11 Law of Reflection Incident angle = Reflected angle We can use this to draw ray diagrams and locate the image of an object

12 The image can be located by tracing reflected rays back to where they seem to come from An image for a flat mirror can be described as: Same Size Upright Virtual

13 Ex 1: use a ray diagram to locate the image which eye is the image winking with?

14 Retroreflector on the moon! Three right angles should cause the laser to bounce back directly

15 Exercises P. 214 #1,2,5 Lab p. 215

16 Dispersion Different wavelengths refract more

17 Why is the sky blue? Scattering

18 Refraction of Light

19 The amazing reappearing penny

20 Refraction of light When light enters a slower medium, rays are bent towards the normal The greater the difference in speed, the more rays are bent: The speed ratio in the medium is written as n This is also called the index of refraction, and can be calculated as: c n 0 c

21 Chocolate Lab According to the microwave, the frequency is 2450 MHz The distance between melt spots will be half the wavelength Ex: 7 cm between antinodes c f c ( m) c m s

22 Snell s Law: Lab p. 215 Trace out dish, measure center, draw normal, premeasure incident angles Then fill dish half full and measure refracted angles Graph: find the slope No Questions Conclusion: include slope, improvements

23 Snell s Law: Lab p. 215

24 Snell s Law When light enters a slower medium, rays are bent towards the normal The greater the difference in speed, the more rays are bent: n sin n sin Recall n can be calculated as: c n 0 c

25 Snell Come listen and learn, I ve a story I tell I sing of the genius of Willebrord Snell A mathematician who lived long ago In the Netherlands where the Rhine river does flow He set for his mind occupations of worth Improved navigation and measured the Earth! He gave us the sine law, that wonderful guy And he made more precise calculation of pi! Singin n 1 sin 1 (hey hey hey) = n 2 sin 2, hip hooray!

26 His greatest feat came in Sixteen Twenty-one When optics as science was really begun! While flashes of lightning illumined his page He wrote down Snell s law, his great gift to the age! So if you wear glasses or like to fry ants Be grateful your lenses were not made by chance! Astronomers hail him with each new-found star! Microscopists toast him from each sleazy bar! Singin n 1 sin 1 (hey hey hey) = n 2 sin 2, hip hooray!

$Now some credit Harriot, others Descartes Both studied refraction, and both were real smart.$

27 Now some credit Harriot, others Descartes Both studied refraction, and both were real smart. But we prefer Willebrord van Roijen Snell He laid down the law, and he did it darn well! Singin n 1 sin 1 (hey hey hey) = n 2 sin 2, hip hooray!

28 Where do you aim the spear? n Given that the hunter observes the light exiting the water at an angle of 35, can we calculate to find the actual position of the fish? sin n sin n sin 1 2 sin n 1 2 2

29 Where do you aim the spear? n sin 1 2 n sin n 1 sin n1 sin sin35 sin

30 Finish labs, hand them in Exercises p. 218 #1-4

31 Ex: #1 p. 218 Light entering a block of glass at 18.5 degrees goes in at 12 degrees find the index of refraction for this glass n sin n sin n 2 n sin sin n sin18.5 sin12

32 Which color refracts more?

33 Total Internal Reflection What happens as we increase the angle of incidence for light going into a less optically dense medium? The refracted ray gets bent further and further from the normal.

34 Critical Angle The transition point between refraction and reflection is for a refraction angle of 90 Solving Snell s law for critical angle gives: n n1sin sin n sin c 1 sin 1 n 2 n n sin c 2 n sin1 n 2 1 c 48. 6

35 Exercises p. 221 #1-4 Optics quiz tomorrow: 3 MC: do you know the difference between diffraction, refraction, reflection? 1 WR: Snell s Law question

36 Curved Mirrors Incoming rays parallel to the axis are reflected through the focal point F Conversely, rays through the focus would be reflected parallel to the axis The focus is located at half the distance to the center of curvature C Rays through C are reflected straight back

37 Image for a concave mirror C F

38 Another Image C F

39 Yet Another Image C F

40 Yet Another Image C F

42 Convex Mirrors Parallel Rays are reflected as though they came from the focus Conversely, rays headed towards the focus are reflected parallel Rays headed towards C are reflected straight back

43 Image for a Convex Mirror F C

45 Lens Activity Concave lens Near Medium Far Image Type SUV SIR LIR LUV Convex Lens Near Medium Far

46 Far x Lens Activity Concave lens Near Medium Far Image Type SUV SIR LIR LUV x x x Convex Lens Near x Medium x

47 Convex (converging) lenses Very similar rules to concave (converging) mirrors: Incoming rays parallel to the axis are refracted through the focal point F Conversely, rays through the focus would be refracted parallel to the axis Rays through the center are transmitted straight through (for thin lenses)

48 Image for a convex lens 2F F F 2F

49 More convex lens 2F F F 2F

50 More convex lens 2F F F 2F

51 Concave (diverging) lens Parallel Rays are refracted as though they came from the focus Conversely, rays headed towards the focus are refracted parallel Rays headed towards center of the lens are transmitted straight through

52 Image for a Concave Lens 2F F F 2F

53 Image for a Concave Lens 2F F F 2F

54 Lens equation d o d i f Where: d o is the object distance, d i is the image distance, and f is the focal length Ex: find the location of the image for an object 55 cm away from a lens with a focal length of 23 cm

55 Ex: find the location of the image for an object 55 cm away from a lens with a focal length of 23 cm 1 d o 1 d i 1 f d f d i o di f d o 1 di m

56 Ex: find the location of the image for an object 25 cm away from a lens with a focal length of 13 cm 1 d o 1 d i 1 f d f d i o di f d o 1 di m

57 Try it! Find the location of the image for an object 25 cm away from your lens, compare to calculations d o d i f

58 Test Yourself p. 237 Choose 5 Chapter Review Page 274 Open book Quizzam tomorrow Start Modern Physics next week Final Exam Jan 23

GEOMETRIC OPTICS. LENSES refract light, so we need to know how light bends when entering and exiting a lens and how that interaction forms an image.

$GEOMETRIC OPTICS. LENSES refract light, so we need to know how light bends when entering and exiting a lens and how that interaction forms an image.$ I. What is GEOMTERIC OPTICS GEOMETRIC OPTICS In geometric optics, LIGHT is treated as imaginary rays. How these rays interact with at the interface of different media, including lenses and mirrors, is