1. blue skies and rainbows! Let’s re-group and re-view
Light Effects
blue skies and rainbows!
Let’s re-group and re-view

2. We pulled a Friday…so let’s review.
Before we can – we need to step back and take a look at our eye:

3. Cornea – transparent covering, helps focus the light
Iris – colored part that controls the amount of light that enters
Pupil – opening that appears black
Lens – focuses light onto retina
Retina – tissue on the back of the eye
Rods - brightness receptors, see in the dark
Cones - color receptors
Optic nerve – carries info to your brain, cause the blind spot

4. More on eye issues to come…
We will review the various “near sighted” and “far sighted” issues and how physics can help us understand our eye appointments when we draw lens diagrams next week.

5. Incandescent vs Fluorescent
Regular light
Enhancing red + green = yellow
Enhancing blue = blue
Things have color because light reflects off them. If white light is shined on these blocks, they appear different colors.
When the same blocks are lit with red and green light, you can’t see any blue…
When the same blocks are lit with only blue light, they all appear blue.

6. Incandescent bulbs enhance red Fluorescent bulbs enhance blue
Objects can reflect only the light that is present. For example, candlelight is yellowish making objects appear different. Incandescent bulbs emit more low frequency light which enhances things that are red. Fluorescent light enhances blue and the sun is all together different too.
Incandescent bulbs enhance red Fluorescent bulbs enhance blue

7. To save energy costs, find the bulbs with the light output you need, then choose the lowest watts.
Brightness is based on LUMENS not WATTS.

8. Same brightness
Lasts longer
Uses less energy
Cost more originally but saves in two ways, last longer and uses less energy when it is on.

9. Why don’t people buy energy efficient bulbs?

10. When the medium changes, light can
absorb (stop)
reflect (return back through the same medium)
transmit (continue on to the new medium)
refract (bend because of changes in speed)
disperse (refract differently for each color)
diffract (bend around a hole)
polarize (transverse wave effect)
or a combination of 1−3.

11. (b) Dispersion

12. Dispersion is the separation of light into different colors
occurs because different colors have slight changes in the speed of light (and thus different indices of refraction).
"Red Refracts Rarely"
"Blue Bends Best"
Red has a longer wavelength than violet and therefore refracts differently.
When white light enters a prism, red is refracted at a smaller angle than violet light.

13. Why is the sky blue?
red sunsets
lots of
blue

14. Rainbows
Inside the raindrop…
Refraction
Reflection
Dispersion

15. "Red Refracts Rarely" (outside of rainbow)
"Blue Bends Best" (inside of rainbow)

16. Double Rainbows!

17. Iridescence
is a rainbow-like effect caused by reflection off of a thin layer (film)

18. (c) Diffraction

19. Diffraction is the bending of a wave around the corner of a hole.
The smaller the hole, the more the wave bends.

20. Light: Particle or Wave?
Who?
Newton
Huygens
Einstein
Reflection
yes
Refraction
Diffraction no
Momentum

21. Diffraction Grating
is a piece of plastic with parallel holes cut into it
Light is bent into a "diffraction pattern"
(lab 227 Tuesday)

22. (d) Polarization

23. Polarization Light is a transverse wave.
Luminous sources give off light in all transverse directions (unpolarized).
A "polarizing filter" (or polarizer or polaroid) makes light go in one transverse direction.
A second polarizer in the same direction passes light; at a right angle blocks light.

24. Glare and Sunglasses
Glare is the light reflecting off a horizontal surface. It is horizontally polarized.
Polarized sunglasses are vertical polarizers; they block the horizontal glare, and pass some of the unpolarized light you want to see.

25. Laser Light Amplification by Stimulated Emission of Radiation
One color (monochromatic), crests occur at same time (coherent), narrow beam (collimated)

26. Laser Safety Always know where your beam is going.
Never point towards faces or eyes.
If only one person can see the beam, it is strong enough to blind.
Turn off when you are done.

27. Doppler Effect moving towards moving away higher frequency
lower frequency
shorter wavelength
longer wavelength
blue shift
red shift

28. Parallax
The apparent shift of an object against a background due to a change in observer position.

29. 3D Movies and TV
How does 3d polarization work? min
Polarized light_3dmovies
3min

30. Reflection and Refraction

31. Changes in the Medium
When light travels through the same medium, it travels in a straight line.
When the medium changes, light can
absorb (stop)
reflect (return back through the same medium)
transmit (continue on to the new medium)
refract (bend because of changes in speed)
disperse (refract differently for each color)
diffract (bend around a hole)
polarize (transverse wave effect)
or a combination of 1−3.

32. Absorbption, Reflection, Transmission

33. Light can … Reflect Refract Absorb The three fates of light are:
reflection (scattering is a form of reflection) bouncing off a surface
refraction (transmission) going through a material
absorption (energy is converted to heat)

34. Absorbtion

35. Absorbtion Opaque objects absorb all light; no light passes through.
Translucent objects absorb some light, and scatter the other light so it does not pass through clearly.
Transparent objects pass light through.
Colored objects absorb some colors of light; the other colors are reflected or transmitted.

36. Reflection

37. Specular – reflection off smooth surfaces
Diffuse – reflection in many directions from a rough surface
A beam can be thought of as a bundle of individual light rays which are traveling parallel to each other. Each individual light ray follows the law of reflection. If the bundle of light rays is incident upon a smooth surface, then the light rays reflect and remain concentrated in a bundle upon leaving the surface. On the other hand, if the surface is microscopically rough, the light rays will reflect in many different directions. Each individual ray follows the law of reflection. However, the roughness of the material means that each ray meets a surface with a different orientation. The normal line is different for different rays. When the individual rays reflect according to the law of reflection, they scatter in different directions.
Five incident rays (labeled A, B, C, D, and E) approach a surface. The normal line (approximated) at each point of incidence is shown in black and labeled with an N. In each case, the law of reflection is followed, resulting in five reflected rays (labeled A, B, C, D, and E,). Notice the blue incident rays are parallel, but the red reflected rays are not. A mirror would be an example of a specular reflector. A sheet of paper is an example of a diffuse reflector.
DVD demo diffuse vs specular reflectors
and angle in = angle out

38. Sound Reflection Echo: a reflection of sound
Reverberation: persistence of sound due to multiple reflections
You have to take the reflection of sound into account with building auditoriums.
What is the reflection of sound called? Echo
If there are multiple reflections of sound cause the sound to persist, what is that called? Reverberation
Reverberation – persistence of sound due to multiple reflections

39. Measuring Reflection
incident ray: the incoming ray of light (draw solid with arrow heads)
reflected ray: the outgoing ray of light (draw solid with arrow heads)
reflection point: where the incident and reflected rays hit the mirror
normal line: passes through the reflection point, and makes a right angle to the mirror (draw dotted)
angle of incidence, θI: angle between the incident ray and the normal line.
angle of reflection, θR: angle between the reflected ray and the normal line.

40. Angles are always measured to the normal line.
never to the mirror!

41. Normal line Angle of incidence Angle of reflection WRONG ANGLE!
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
WRONG ANGLE!
WRONG ANGLE!
A normal is a line perpendicular to the surface.
In the diagram, the ray of light approaching the mirror is known as the incident ray.
The ray of light which leaves the mirror is known as the reflected ray.
The angle between the incident ray and the normal is known as the angle of incidence.
The angle between the reflected ray and the normal is known as the angle of reflection.
The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
Simple put: angle in=angle out.
DVD demo diffuse vs specular reflectors and angle in = angle out
Reflection
point

42. Angles are always measured to
the normal line.

43. Law of Reflection
The angle of incidence equals the angle of reflection:
θI = θR

44. Specular – reflection off smooth surfaces
Diffuse – reflection in many directions from a rough surface
A beam can be thought of as a bundle of individual light rays which are traveling parallel to each other. Each individual light ray follows the law of reflection. If the bundle of light rays is incident upon a smooth surface, then the light rays reflect and remain concentrated in a bundle upon leaving the surface. On the other hand, if the surface is microscopically rough, the light rays will reflect in many different directions. Each individual ray follows the law of reflection. However, the roughness of the material means that each ray meets a surface with a different orientation. The normal line is different for different rays. When the individual rays reflect according to the law of reflection, they scatter in different directions.
Five incident rays (labeled A, B, C, D, and E) approach a surface. The normal line (approximated) at each point of incidence is shown in black and labeled with an N. In each case, the law of reflection is followed, resulting in five reflected rays (labeled A, B, C, D, and E,). Notice the blue incident rays are parallel, but the red reflected rays are not. A mirror would be an example of a specular reflector. A sheet of paper is an example of a diffuse reflector.
DVD demo diffuse vs specular reflectors
and angle in = angle out

45. Other uses of reflectors…
Periscope
Car headlight
Down Periscope, and the captain spins around.
Car Headlights have reflectors to make your lights seem brighter.

46. Refraction

47. Refraction
is the change in direction of a wave as it moves between two mediums in which the wave travels at different speeds.
toy car video
fish tank demo

48. Refraction Toy car analogy Marching soldiers analogy!
What happens next can be visualized by considering a marching band. Imagine a row of band members marching side-by-side. When they want to make a turn, the members at one end of the row walk slower than the members at the other end of the row. The row spins around, with the slow-walking members at the inner part of the turn.

49. Measuring Refraction incident ray: (same)
refracted ray: the outgoing ray of light
refraction point: where the incident and refracted rays hit the lens
normal line: passes through the refraction point, and makes a right angle to the lens
angle of incidence, θI: (same).
angle of refraction, θR: angle between the refracted ray and the normal line.

50. Angles are always measured to
the normal line.

51. How much light refracts depends…
the angle the light enters
type of materials
In water, light travels at .75c.
In glass, light travels at .67c. (depending on the type of glass and the temperature)

52. air  less dense medium  light is faster 
light bends away from the normal
glass  more dense medium  light is slower 
light bends toward the normal

53. Index of Refraction, n: the ratio of the velocity of light in a vacuum to that in a medium [no units]
n = index of refraction
c = speed of light in vacuum
= 3.0 x 108 [m/s]
v = speed of light in given medium
↓speed of light = ↑ n value
slower light travels = the higher the index of refraction

54. Example: If light travels at 1
Example: If light travels at 1.90x108 [m/s] in crystal, what is the crystal’s index of refraction?

55. nr = refracted index of refraction
Snell’s Law
θi = angle of incidence θr = angle of refraction ni = incident index of refraction
nr = refracted index of refraction
Like with reflection, refraction also involves the angles that the incident ray and the refracted ray make with the normal to the surface at the point of refraction.
Unlike reflection, refraction also depends on the media through which the light rays are traveling. This dependence is made explicit in Snell's Law via refractive indexes, numbers which are constant for given media.
As in reflection, we measure the angles from the normal to the surface, at the point of contact. The constants n are the indices of refraction for the corresponding media.

56. Substance
(n)
Air
1.00
Water
1.33
In the picture below, light is traveling from water into air. The angle of incidence is 30°. What angle of refraction?
ni sinӨi = nr sinӨr
1.33 sin 30° = 1.00 sinӨr
1.33 sin 30° =sinӨr
1.00
This is a index of refraction chart, different materials have different “n” values.
Lets do an example:
We shine a light of wavelength 600 nm from water into air, so that it makes a 30 angle with the normal of the boundary. Suppose we wish to find the angle x that the outgoing ray makes with the boundary.
We use Snell's Law
Make sure your calculator is in degrees and not radians
Explain how to do on calculator with sin-1
1.33 sin 30 = sin x x = 41o
Өr = sin
Өr = 41°

57. Is the fish higher or lower than it appears?
It is hard to go spear fishing because of refraction (also because it is illegal).
Is the fish higher or lower than it appears? The fish is lower than it appears. You think light is traveling in a straight line so your eye tricks you in a way.
lower

58. critical angle – incident angle that causes the refracted ray to lie along the boundary
total internal reflection – occurs when the incident angle is greater than the critical angle

59. Fiber Optics
demo

60. Internal Reflection is what makes a diamond sparkle

61. Sound Refraction – sound travels faster in warm air

62. Mirage – image that appears in the distance due to the refraction of light

63. Prezi “now you see me” http://prezi.com/jtbjhlaqv3nd/untitled-prezi/
Colors
Bill Nye (6min)

64. refraction http://www.youtube.com/watch?v=1Ppjl0iKFnE
Aim at the tail of the fish
Is your red my red? (9min)