1. Reflection and Refraction
Optics
Reflection and Refraction

2. Reflection
When a wave encounters a new medium or barrier some of the wave is bounced back (reflected), and some is transmitted (refracted)

3. Law of Reflection Angle of Incidence = Angle of Reflection θi = θr
Always measured from Normal(Perpendicular) θi θr

4. Image Types Real – Light rays actually travel to that location
Virtual – Light appears to be at that location
Upright – image is right side up compared to object
Inverted – image is upside down as compared to object

5. Plane Mirror Flat, smooth surface from which light is reflected.
The distance the object is away from the mirror is equal to the distance the image appears to be “in” the mirror

6. Plane (flat) Mirror
Mirror

8. Huygens Principle
Every point on a propagating wave front serves as a source of a spherical secondary wavelet
The corresponding spherical wavelets produce further wave fronts
Basis for Diffraction, Reflection, Refraction

9. Huygens Principle

10. Huygens Principle

11. Huygens Principle First proposed explanation that light is a wave
Newton later proposed that light is a particle

12. Question
Compared to running down the road, if you were to run in thick mud….
Would you go as fast? Speed decreases
Would your steps be as long? Wavelength decrease

13. Refraction
Changing of speed when wave enters new material (frequency remains constant)
Speed decreases in more dense material
Wavelength decreases
Speed increases in less dense material
Wavelength increases

14. Refraction Example
Freqair=Freqwater because the color remains the same
Since the wavelength changes, the velocity must change proportionately
Air
Water

15. Index of Refraction (n)
Measure of the optical density of a material
Table in the Reference Tables

16. Refraction When a wave enters a new medium, it changes speed.
When a wave enters a new medium, it changes direction
Simulation

17. Refraction

18. Refraction

19. Snell’s Law
n1 sin θ1 = n2 sin θ2
Air
Water θi θr

20. Snell’s Law
When a wave enters a more dense material, the wave will bend TOWARDS the normal
When a wave enters a less dense material, the wave will bend AWAY from the normal

21. Example n1 sin θ1 = n2 sin θ2 θr= 58.7° Air Water n = 1.00 n = 1.33
40°

23. Example θi= 47° θr= 76.6° θi= 48° θr= 81.3°
Air
Water
n = 1.00
n = 1.33
θi= 47° θr= 76.6°
θi= 48° θr= 81.3°
θi= 49° θr= ? Is there a problem?
θr=?

24. Total Internal Reflection
At a certain incident angle the refracted ray will be at 90°.
Critical Angle,θc
At angles greater than the Critical Angle, the ray is reflected back into the material. θi
Air
Water
n = 1.00
n = 1.33 θr

25. Total Internal Reflection
n1 sin θC = n2 sin θ2
sin θ2 = 1
n1 sin θC = n2
n1 > n2

27. Dispersion Spreading of light into its color components
Index of refraction is based on frequency of light
Index varies for different frequencies

28. Dispersion

30. Curved Mirrors and Lenses

31. Vocabulary Object distance, do Image distance, di
Distance object is from optical device
Image distance, di
Distance image is from optical device

32. Vocabulary Object Height, ho Image Height, hi Height of object
Height of image

33. Vocabulary
Real Image
Image formed by actual intersection of light rays
Image can be projected on a screen
di=(+)

34. Vocabulary Virtual Image (imaginary) Light rays do not intersect
Image can NOT be projected on screen
The eye traces back the rays to where they appeared to have once intersected
di=(-)

35. Vocabulary Upright Image Inverted Image
Object
Image
Upright Image
Image is of the same orientation as object
hi = (+)
Inverted Image
Image is inverted from the orientation of the object
hi = (-)
Object
Image

36. Vocabulary Magnification, M
Ratio of the image height to the object height
M=(+) image is upright
M=(-) image is inverted

37. Plane Mirror
Mirror
do = -di
ho=hi
M=1

39. Spherical Mirrors Concave Mirrors Convex Mirrors
Mirror surface is on the inside of the curve
Convex Mirrors
Mirror surface is on the outside of the curve

40. Focal Point
Point where light converges
Half the radius f C

41. Concave Mirror
Ray that is initially parallel to central axis reflects through focal point
Ray that is initially through focal point reflects parallel to central axis
Ray that is incident at vertex, reflects at same angle
Ray that travels through center of curvature will reflect back through center of curvature

42. Concave Mirror f C

43. Mirror Equation

44. Example f C
do = 30 cm
f = 10 cm
di = ?
di = 15 cm
M = -0.5

45. Convex Mirror
Ray that is initially parallel to central axis reflects through virtual focal point
Ray that is initially through virtual focal point reflects parallel to central axis
Ray that is incident at vertex, reflects at same angle
Ray that travels through center of curvature will reflect back through center of curvature

46. Example f C

47. Example
di = ?
f = -10 cm
do =15 cm
di = -6 cm
M = 0.4

49. Lenses Converging Lenses Diverging Lenses Biconvex f=(+) Biconcave

50. Converging Lens Rays
Ray that is initially parallel to central axis will refract through far focal point
Ray that is initially through near focal point will refract parallel to central axis
Ray that passes through center of lens pass without refraction

51. Converging Lens

52. Converging Lens Example
f = 10 cm
di= ?
do = 20 cm
di= 20 cm
M = 1

53. Diverging Lens Rays
Ray that is initially parallel will refract as if coming from near focal point
Ray that is initially through far focal point will refract as if coming from parallel
Ray that passes through center will continue on

54. Diverging Lens

55. Diverging Lens Example
do = 25 cm
f = -10 cm
di = ?
di = cm
M = 0.3

56. Lenses in Combination
Image from the first lens becomes the object for the second lens

57. Lenses in Combination

58. Lenses in Combination do1 = 25 cm f2 = 8 cm di2 = 12 cm f1 = 10 cm