1. Chapter 18
Light

2. White Light – entire range of colors on visible spectrum - ROYGBIV
Bad: Causes skin cancer
Good: produces vitamin D, kills bacteria on surgical tool
Warms you from the sun – skin absorbs wave
Used to treat cancer
AM – amplitude modulation
FM- Frequency modulation
White Light – entire range of colors on visible spectrum - ROYGBIV

3. What is Light? Light is an electromagnetic wave
Vibration of an electric field and magnetic field together
Electromagnetic waves can travel through space or matter

4. What is Visible Light? Light travels at 300,000,000 m/s!
It takes 8.3 minutes to travel from the sun to the earth
It can travel around the earth 7 times in 1 sec

5. Interactions of Light Waves
Reflection
The bouncing back of a wave when that ray hits a surface that it does not go through

6. Reflection or Light Source
The moon
Does not produce its own light
Illuminated by the reflection
of the sun
Visible object w/o its own light source
Firefly
Luminous
Produces its’ own light

7. Absorption and Scattering Light
Absorption- when a light beam shines through the air, particles absorb some of the energy – causing the light to be dimmer
Scattering- interaction of light with matter that causes the light to change its energy, direction, or motion

8. Refraction
Refraction – the bending of a wave as it passes through a material
A prism causes white light to
refract and separate into the
colors of visible light
(ROYGBIV)
Red, Orange, Yellow, Green, Blue, Indigo, Violet

9. Diffraction and Interference
Diffraction – a change in the direction of a wave when it finds an obstacle
Interference – combination of 2 or
more waves that result in a single
wave
Constructive – greater amplitude
Destructive- smaller amplitude

10. Light and Color Transmission – the passing of light through matter
Transparent – allows light to pass
Translucent – transmits but also
scatters light
Opaque – does not transmit light

11. Opaque Objects Color Objects absorb some light and reflect other
The colors that are reflected determine the color you see

12. Transparent & Translucent
When the object is colored, you see the color of light that was transmitted through the material

13. Colors of Light Color Addition – combining colors of light
Primary colors of light – red, blue and green
Color Subtraction – combining colors of pigment
Primary colors of pigment – yellow, cyan and magenta

14. The Law of Reflection Light waves are electromagnetic waves.
Light waves travel from their source in all directions
Light is made up of rays that travel in straight lines.
An arrow, called a ray, is used to show the path and direction of light

15. Mirrors
Law of Reflection – states that the angle of reflection is equal to the angle of incidence.
A ray diagram shows how rays change direction when they strike mirrors and pass through lenses.

16. Mirrors 3 types of mirrors Plane Mirrors Concave mirrors
Flat
Concave mirrors
Indent
Convex mirrors
Outdent

17. Plane Mirror Plane Mirrors have a flat surface.
Light reflects off a mirror because it can not pass through the surface.
The reflection of an object in a plane mirror is right side up and the same size as the object, but reversed left to right.
Plane mirrors form virtual images. A virtual image is an image through which light does not travel

19. Ray Diagrams
We use ray diagrams to show how light changes as it strikes mirrors or passes through lenses
Light rays
Going in? Green!
Reflecting out? Red!

20. Intersections will give you the image location!
Plane Mirror Ray Diagrams
First, we draw an image of the object on the other side of the mirror
Distance A is equal to distance B and the image size is the same size as the object size.

21. Intersections will give you the image location!
Plane Mirror Ray Diagrams
Second, we draw light rays from the image to the eye
The image is virtual. Broken lines from the image to mirror indicate virtual rays. Virtual image: Light rays do not actually meet at the image position. Because of that, a virtual image cannot be projected on a screen.
Continuous lines from the mirror to eye indicate the reflected rays.

22. Intersections will give you the image location!
Plane Mirror Ray Diagrams
Third, we join the light rays from the mirror to the object
Lines joining the object to the positions of the reflected rays on the mirror represent the incident rays by following the law of reflection.

23. L.O.S.T. Mirror Images How can I easily describe the image formed?

24. L.O.S.T
L- Location: location of the image (in front or behind the mirror).
O- Orientation: which way the image is oriented compared to the original object (upright or inverted).
S- Size: compared to original object is it same size, smaller or bigger?
T- Type: is the image a real image or virtual image?

25. Plane Mirrors Characteristics of a plane mirror image:
L:Object distance from mirror = image distance from mirror
O: Orientation is ALWAYS upright
S: Object size = Image Size
T: ALWAYS forms a virtual image
Image is reversed- left to right

26. Plane Mirror
Let’s try! L: O: S: T:

27. Plane Mirror L: O: S: T:
Let’s try!

28. Plane Mirrors Partner Share
How does the LOST description compare for both of the images produced by plane mirrors?

29. Concave Mirrors
A concave mirror is curved inward. They can produce both a virtual or a real image.
Real images are in front of the mirror
The point at which light rays meet is called the focal point.

30. Concave Mirror Can make small objects appear larger
Ex: Make-up mirrors, shaving mirrors

31. How Images Are Formed in Concave Mirrors

32. Concave Mirrors When does it make a real image?
Object has to be farther away (behind) from the focal point
When does it make a virtual image?
Object has to be closer to (in front of) the focal point

33. Concave Mirrors “OUTSIDE“ the focus C F
Moving towards the focus, the image is REAL, inverted. It could be smaller, the same size, or larger than the image (depending on the object location)

34. Intersection will give you the image location!
Concave Mirror Ray Diagrams
Pick a point on the top of the object and draw two incident rays traveling towards the mirror.
Using a straight edge, accurately draw one ray so that it passes exactly through the focal point on the way to the mirror. Draw the second ray such that it travels exactly parallel to the principal axis. Place arrowheads upon the rays to indicate their direction of travel.

35. Intersection will give you the image location!
Concave Mirror Ray Diagrams
Once these incident rays strike the mirror, reflect them according to the two rules of reflection for concave mirrors.
The ray that passes through the focal point on the way to the mirror will reflect and travel parallel to the principal axis. Use a straight edge to accurately draw its path. The ray that traveled parallel to the principal axis on the way to the mirror will reflect and travel through the focal point. Place arrowheads upon the rays to indicate their direction of travel. Extend the rays past their point of intersection.

36. Intersection will give you the image location!
Concave Mirror Ray Diagrams
Find the location of the bottom of the object
If the bottom of the object lies upon the principal axis (as it does in this example), then the image of this point will also lie upon the principal axis and be the same distance from the mirror as the image of the top of the object. At this point the entire image can be filled in.

37. Concave Mirrors
What image was formed? L: O: S: T:

38. Concave Mirrors
Let’s try! L: O: S: T:

39. Concave Mirrors
Let’s try! L: O: S: T:

40. Concave Mirrors “INSIDE” the focus C F
Moving towards the mirror, the image is VIRTUAL, UPRIGHT, and gets smaller (although the image is ALWAYS larger than the object itself).

41. Concave Mirrors
Let’s try! L: O: S: T:

42. Concave Mirrors
Let’s try! L: O: S: T:

43. Smaller or same size as object
Concave Mirror
Characteristics of a Concave mirror image:
Location of Object
Location of Image
Orientation of Image
Size of Image
Type of Image
Past F
In front of mirror
Inverted
Smaller or same size as object
Real
Between mirror and F
Behind mirror
Upright
Larger than object
Virtual

44. Concave Mirrors Partner Share
How does the LOST description compare for both of the images produced by concave mirrors?

45. Convex Mirror
A convex mirror is bent outward. The object is virtual and appears smaller and upright.
Convex mirrors spread out light.

46. Convex Mirrors Can make large objects appear smaller (see a WIDE view)
Ex: Security mirrors, driveway mirrors, car door mirrors

47. Convex Mirror Characteristics of a convex mirror image:
L: Image is ALWAYS behind mirror
O: Orientation is ALWAYS upright
S: Object size > Image Size
T: ALWAYS forms a virtual image

48. Note: All rays want to pass through F, but none do
Convex Mirrors
Note: All rays want to pass through F, but none do
F C
C’ F’
When an object gets closer to the mirror, its image is VIRTUAL, UPRIGHT, and keeps getting smaller (and the images are always smaller than the object).

49. Intersection will give you the image location!
Convex Mirror Ray Diagrams
Pick a point on the top of the object and draw two incident rays traveling towards the mirror.
Using a straight edge, accurately draw one ray so that it travels towards the focal point on the opposite side of the mirror; this ray will strike the mirror before reaching the focal point; stop the ray at the point of incidence with the mirror. Draw the second ray such that it travels exactly parallel to the principal axis. Place arrowheads upon the rays to indicate their direction of travel.

50. Intersection will give you the image location!
Convex Mirror Ray Diagrams
Once these incident rays strike the mirror, reflect them according to the two rules of reflection for convex mirrors.
The ray that travels towards the focal point will reflect and travel parallel to the principal axis.
The ray that traveled parallel to the principal axis on the way to the mirror will reflect and travel in a direction such that its extension on the other side of the mirror passes through the focal point. Align a straight edge with the point of incidence and the focal point, and draw the second reflected ray. Place arrowheads upon the rays.

51. Intersection will give you the image location!
Convex Mirror Ray Diagrams
Locate and mark the image of the top of the object.
The image point of the top of the object is the point where the two reflected rays intersect. Since the two reflected rays are diverging, they must be extended behind the mirror in order to intersect. Using a straight edge, extend each of the rays using dashed lines. Draw the extensions until they intersect. The point of intersection is the image point of the top of the object. Both reflected rays would appear to diverge from this point.

52. Intersection will give you the image location!
Convex Mirror Ray Diagrams
Find the location of the bottom of the object
If the bottom of the object lies upon the principal axis (as it does in this example), then the image of this point will also lie upon the principal axis and be the same distance from the mirror as the image of the top of the object. At this point the complete image can be filled in.

53. Convex Mirror
Let’s try! L: O: S: T:

54. Convex Mirror
Let’s try! L: O: S: T:

55. Convex Mirror Partner Share
How does the LOST description compare for both of the images produced by convex mirrors

56. Mirrors – reflect light
Types of Mirrors
Images Formed
Virtual or Real
Direction of Image
Plane / Flat
Virtual
Upright/opposite
Convex
(Curves outward)
Upright/smaller
Concave
(curves inward)
Object – Focal- Mirror
Real
Upside down
Focal- Object- Mirror
Upright

57. Refraction
The index of refraction for a material is the ratio of the speed of light in a vacuum to the speed of the light in the material.
When light enters a new medium at an angle, the change in speed causes the light to bend or refract.

58. Lenses
Lens – an object made of transparent material that has one or two curved surfaces that can refract or bend light.
The curvature and thickness of a lens affect the way it refracts light.

59. concave lens = divergent lens
A concave lens is curved inward at the center (thinnest) and the thickest part at the outside edges.
The light rays are spread out.
Forms a small, upright virtual image.
Concave lenses cure nearsightedness when an eyeball is too long
Examples: a peep hole in a door,
found in viewfinders
of cameras, eyeglasses,
telescopes.
concave lens = divergent lens

60. Image Formation in Concave Lenses

61. Intersection will give you the image location!
Concave lens
Concave Lens Diagrams
Pick a point on the top of the object and draw two incident rays traveling towards the lens.
Draw one ray so that it travels towards the focal point on the opposite side of the lens; stop the ray at the point of incidence with the lens.
Draw the second ray such that it travels exactly parallel to the center line.
Add arrowheads

62. Intersection will give you the image location!
Concave Lens
Concave Lens Diagrams
Once these incident rays strike the lens, refract them according to the rules of refraction
The ray that travels towards the focal point will refract through the lens and travel parallel to the center line.
The ray that traveled parallel to the principal axis on the way to the lens will refract and travel in a direction such that its extension passes through the focal point on the object's side of the lens.
Place arrowheads upon the rays to indicate their direction.

63. Intersection will give you the image location!
Concave Lens
Concave Lens Diagrams
Locate and mark the image of the top of the object.
Since the refracted rays are diverging, they must be extended behind the lens in order to intersect.
Using a straight edge, extend each of the rays using dashed lines. Draw the extensions until they intersect.
The point of intersection is the image point of the top of the object.
Draw the image in

64. Intersection will give you the image location!
Concave Lens
Concave Lens Diagrams
Draw in the image
If the bottom of the object lies upon the principal axis (as it does in this example), then the image of this point will also lie upon the principal axis and be the same distance from the mirror as the image of the top of the object. At this point the complete image can be filled in.

65. Concave Lens
Let’s try! L: O: S: T:

66. convex lens = converging lens
A convex lens is curved outward at the center and is thinnest at the outer edge.
Convex lenses form either real or virtual images.
If the object is located between a convex lens and its focal point it forms an enlarged virtual image
If the object is located behind the focal point, it forms a smaller real image
The real images is upside down.
Example; microscopes, magnifying glasses, eye glasses.
Convex lenses can be used to correct farsightedness when an eyeball is too short
convex lens = converging lens

67. Image Formation in Convex Lenses

68. Intersection will give you the image location!
Convex Lens
Convex Lens Diagrams
Pick a point on the top of the object and draw two incident rays traveling towards the lens.
Using a straight edge, accurately draw one ray so that it passes exactly through the focal point on the way to the lens.
Draw the second ray such that it travels exactly parallel to the center line.
Add arrowheads

69. Intersection will give you the image location!
Convex Lens
Convex Lens Diagrams
Once these incident rays strike the lens, refract them according to the rules of refraction for converging lenses.
The ray that passes through the focal point will refract and travel parallel to the principal axis.
The ray that traveled parallel to the principal axis on the way to the lens will refract and travel through the focal point.
Place arrowheads upon the rays to indicate their direction

70. Intersection will give you the image location!
Convex Lens
Convex Lens Diagrams
Mark the image of the top of the object.
If the bottom of the object lies upon the principal axis (as it does in this example), then the image of this point will also lie upon the principal axis and be the same distance from the mirror as the image of the top of the object. At this point the entire image can be filled in.

71. Convex Lens
Let’s try! L: O: S: T:

72. Convex Lens
Let’s try! L: O: S: T:

73. Convex Lens Partner Share
How does the LOST description compare for both of the images produced by convex lenses?

74. Type Real / Virtual Upright/ Upside-down Smaller/Larger
Plane Mirror
Virtual
Upright
(Reversed)
Same
Concave Mirror
(Behind focal pt)
Real
Upside down
Depends on location
(In front of focal pt)
Convex Mirror
Smaller
Concave Lens
(b/twn focus & lens)
Convex Lens
Larger

75. Light & Sight The Human Eye
Cornea: Protective “Window” of
eye
Iris: Colored part that acts like a
camera shutter.
Pupil: Hole in the middle of the
iris.
Lens: has adjustable focal length.
Retina: Where image is formed.
Optic nerve: Sends image to
brain where it is flipped
upside down.
Light & Sight The Human Eye
Muscles that “tense” the lens

76. Eye Problems
Nearsightedness - The eyeball is too thick, causing the image to focus in front of the retina. A person can't see distant objects, but can see near objects well. A concave lens can be used to correct this problem.
Farsightedness - The eyeball is too thin, causing the image to focus behind the retina. A person can see distant objects clearly, but has difficulty with near objects. A convex lens can be used to correct this problem.