1. Conceptual Physics Fundamentals
Chapter 13:
LIGHT WAVES

2. This lecture will help you understand:
Electromagnetic Spectrum
Transparent and Opaque Materials
Color
Why the Sky is Blue, Sunsets are Red, and Clouds are White
Diffraction
Interference of Light

3. Light Waves
“The light of stars that were extinguished ages ago still reaches us. So it is with great men who died centuries ago, but still reach us with the radiations of their personalities.” —Kahlil Gibran

4. Light Waves Light is the only thing we can see
originates from the accelerated motion of electrons
electromagnetic phenomenon

5. Electromagnetic Spectrum
Electromagnetic wave
made up of vibrating electric and magnetic fields

6. Electromagnetic Spectrum
CHECK YOUR NEIGHBOR
If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave with a
A. period of 1000 seconds.
speed of 1000 m/s.
wavelength of 1000 m.
none of the above
D. none of the above.

7. Electromagnetic Spectrum
CHECK YOUR ANSWER
If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave with a
A. period of 1000 seconds.
speed of 1000 m/s.
wavelength of 1000 m.
none of the above
Explanation:
The vibrating electron would emit a wave with a frequency of 1000 Hz, which is not in the list above.
D. none of the above.

8. Electromagnetic Spectrum
classification of electromagnetic waves according to frequency
lowest frequency of light we can see appears red
highest frequency of light we can see appears violet
higher frequency of light is ultraviolet—more energetic and causes sunburns
beyond are X-ray and gamma ray
no sharp boundary between regions

9. Electromagnetic Spectrum
CHECK YOUR NEIGHBOR
The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of
A. radio waves.
microwaves.
visible light.
gamma rays.
C. visible light.

10. Electromagnetic Spectrum
CHECK YOUR ANSWER
The electromagnetic spectrum spans waves ranging from lowest to highest frequencies. The smallest portion of the electromagnetic spectrum is that of
A. radio waves.
microwaves.
visible light.
gamma rays.
C. visible light.

11. Which of these is fundamentally different from the others?
Electromagnetic Spectrum
CHECK YOUR NEIGHBOR
Which of these is fundamentally different from the others?
A. sound waves
light waves
radio waves
X-rays
A. sound waves.

12. Which of these is fundamentally different from the others?
Electromagnetic Spectrum
CHECK YOUR ANSWER
Which of these is fundamentally different from the others?
A. sound waves
light waves
radio waves
X-rays
Explanation:
All are electromagnetic waves except sound, which is a mechanical wave.
A. sound waves.

13. Transparent and Opaque Materials
Light is transmitted similar to sound
light incident on matter forces some electrons in matter to vibrate

14. Transparent and Opaque Materials
How light penetrates transparent material such as glass

15. Transparent and Opaque Materials
How light penetrates transparent material such as glass (continued)
electrons or molecules in the glass are forced into vibration
energy is momentarily absorbed and vibrates the electrons in the glass
this vibrating electron either emits a photon or transfers the energy as heat
Time delay between absorption and reemission of energy of vibrating electrons results in a lower average speed of light through a transparent material

16. Transparent and Opaque Materials
Average speed of light through different materials
vacuum—c (300,000,000 m/s)
atmosphere—slightly less than c (but rounded off to c)
water—0.75 c
glass—0.67 c, depending on material
diamond—0.41 c

17. Strictly speaking, the photons of light incident on glass are
Transparent and Opaque Materials
CHECK YOUR NEIGHBOR
Strictly speaking, the photons of light incident on glass are
A. also the ones that travel through and exit the other side.
not the ones that travel through and exit the other side.
absorbed and transformed to thermal energy.
diffracted.
B. not the ones that travel through and exit the other side.

18. Strictly speaking, the photons of light incident on glass are
Transparent and Opaque Materials
CHECK YOUR ANSWER
Strictly speaking, the photons of light incident on glass are
A. also the ones that travel through and exit the other side.
not the ones that travel through and exit the other side.
absorbed and transformed to thermal energy.
diffracted.
Explanation:
Figure 13.6 illustrates this nicely. The light that exits the glass is not the same light that begins the process of absorption and re-emission.
B. not the ones that travel through and exit the other side.

19. Transparent and Opaque Materials
CHECK YOUR NEIGHBOR
Compared with the frequency of illuminating light on a sheet of transparent plastic, the frequency of light that is transmitted
A. is slightly less.
is the same.
is slightly higher.
depends on the type of plastic.
B. the same.

20. Transparent and Opaque Materials
CHECK YOUR ANSWER
Compared with the frequency of illuminating light on a sheet of transparent plastic, the frequency of light that is transmitted
A. is slightly less.
is the same.
is slightly higher.
depends on the type of plastic
Explanation:
Speed of light in plastic may vary, but the frequency transmitted doesn’t.
B. higher.

21. The average speed of light is less in
Transparent and Opaque Materials
CHECK YOUR NEIGHBOR
The average speed of light is less in
A. air before entering glass.
glass.
air after emerging from glass.
none of the above
B. glass.

22. The average speed of light is less in
Transparent and Opaque Materials
CHECK YOUR ANSWER
The average speed of light is less in
A. air before entering glass.
glass.
air after emerging from glass.
none of the above
B. glass.

23. Transparent and Opaque Materials
Reflection
Light shining on metal forces free electrons in the metal into vibrations that emit their own light as reflection.

24. Transparent and Opaque Materials
Light incident on:
dry surfaces bounces directly to your eye
wet surfaces bounces inside the transparent wet region, absorbing energy with each bounce, and reaches your eye darker than from a dry surface

25. Color
Color
physiological experience
in the eye of the beholder

26. Color Color we see depends on frequency of light
lowest frequency—perceived as red
in between lowest and highest frequency—perceived as colors of the rainbow (red, orange, yellow, green, blue, indigo, violet)
highest frequency—perceived as violet
beyond violet, invisible ultraviolet (UV)

27. Color Selective reflection
We see the color of a rose by the light it reflects.

28. Color Objects reflect light of some frequencies and absorb the rest.
rose petals absorb most of the light and reflect red
objects that absorb light and reflect none appear black
object can reflect only those frequencies present in the illuminating light

29. Color
Color of transparent object depends on color of light it transmits.
colored glass is warmed due to the energy of absorbed light illuminating the glass

30. Color Mixed colored lights Distribution of solar frequencies is uneven
most intense in yellow-green portion (where our eyes are most sensitive)

31. Color
Radiation curve divides into three regions that match the color receptors in our eyes.

32. Color Additive primary colors red, green, and blue
produce any color in the spectrum

33. Red, green, and blue light overlap to form
Color
CHECK YOUR NEIGHBOR
Red, green, and blue light overlap to form
A. red light.
green light.
blue light.
white light.
D. white light.

34. Red, green, and blue light overlap to form
Color
CHECK YOUR ANSWER
Red, green, and blue light overlap to form
A. red light.
green light.
blue light.
white light.
D. white light.

35. Color CHECK YOUR NEIGHBOR
When the color yellow is seen on your TV screen, the phosphors being activated on the screen are
A. mainly yellow.
blue and red.
green and yellow.
red and green.
D. red and green.

36. Color CHECK YOUR ANSWER
When the color yellow is seen on your TV screen, the phosphors being activated on the screen are
A. mainly yellow.
blue and red.
green and yellow.
red and green.
D. red and green.

37. A blue object will appear black when illuminated with
Color
CHECK YOUR NEIGHBOR
A blue object will appear black when illuminated with
A. blue light.
cyan light.
yellow light.
magenta light.
C. yellow light.

38. A blue object will appear black when illuminated with
Color
CHECK YOUR ANSWER
A blue object will appear black when illuminated with
A. blue light.
cyan light.
yellow light.
magenta light.
C. yellow.

39. Color Subtractive primary colors
combination of two of the three additive primary colors
red + blue = magenta
red + green = yellow
blue + green = cyan

40. Color The shadows of the golf ball are subtractive
Magenta (opposite of green)
Cyan (opposite of red)
Yellow (opposite of blue)

41. Color Subtractive primaries are complementary to additive primaries.
magenta + green = white = red + blue + green
yellow + blue = white + red + green + blue
example: color printing

42. A red rose will not appear red when illuminated only with
Color
CHECK YOUR NEIGHBOR
A red rose will not appear red when illuminated only with
A. red light.
orange light.
white light.
cyan light.
D. cyan light.

43. A red rose will not appear red when illuminated only with
Color
CHECK YOUR ANSWER
A red rose will not appear red when illuminated only with
A. red light.
orange light.
white light.
cyan light.
D. cyan light.

44. Color
Only three colors of ink (plus black) are used to print color photographs—(a) magenta, (b) yellow, (c) cyan, which when combined produce the colors shown in (d). The addition of black (e) produces the finished result (f).

45. Why the Sky is Blue Why the sky is blue
results of selective scattering of smaller particles than the wavelength of incident light and resonances at frequencies higher than scattered light
the tinier the particle, the higher the frequency of light it will reemit

46. Why the Sky is Blue Why the sky is blue (continued)
due to selective scattering
blue scattered light predominates in our vision
varies in different locations under various conditions
clear dry day—much deeper blue sky
clear, humid day—beautiful blue sky
lots of dust particles and larger molecules than nitrogen and oxygen in the atmosphere—less blue sky with whitish appearance
after heavy rainstorm (washing away of airborne particles)—deeper blue sky

47. A white sky is evidence that the atmosphere contains
Why the Sky is Blue
CHECK YOUR NEIGHBOR
A white sky is evidence that the atmosphere contains
A. predominantly small particles.
predominantly large particles.
a mixture of particle sizes.
pollutants.
C. a mixture of particle sizes.

48. A white sky is evidence that the atmosphere contains
Why the Sky is Blue
CHECK YOUR ANSWER
A white sky is evidence that the atmosphere contains
A. predominantly small particles.
predominantly large particles.
a mixture of particle sizes.
pollutants.
C. a mixture of particle sizes.

49. Why Sunsets are Red
Light that is least scattered is light of low frequencies, which best travel through air.
red
orange
yellow

50. A variety of sunset colors is evidence for a variety of
Why Sunsets are Red
CHECK YOUR NEIGHBOR
A variety of sunset colors is evidence for a variety of
A. elements in the Sun.
apparent atmosphere thickness.
atmospheric particles.
primary colors.
C. atmospheric particles.

51. A variety of sunset colors is evidence for a variety of
Why Sunsets are Red
CHECK YOUR ANSWER
A variety of sunset colors is evidence for a variety of
A. elements in the Sun.
apparent atmosphere thickness.
atmospheric particles.
primary colors.
C. atmospheric particles.

52. Why Sunsets are Red CHECK YOUR NEIGHBOR
If molecules in the sky scattered orange light instead of blue light, sunsets would be
A. orange.
yellow.
green.
blue.
D. blue.

53. Why Sunsets are Red CHECK YOUR ANSWER
If molecules in the sky scattered orange light instead of blue light, sunsets would be
A. orange.
yellow.
green.
blue.
Explanation:
Of the colors listed, blue is closest to being the complementary color of orange.
D. blue.

54. Why Clouds are White Clouds
clusters of various sizes of water droplets

55. Why Clouds are White Size of clusters determines scattered cloud color
tiny clusters produce bluish clouds
slightly large clusters produce greenish clouds
larger clusters produce reddish clouds
overall result is white clouds
slightly larger clusters produce a deep grey
still larger clusters produce raindrops

56. Diffraction Diffraction
bending of waves by means other than reflection and refraction
property of all kinds of waves
seen around edges of many shadows

57. Diffraction Waves diffract after passing through a narrow opening.
Plane waves passing through openings of various sizes. The smaller the opening, the greater the bending of the waves at the edges.

58. Diffraction
Amount of diffraction depends on wavelength of the wave compared to the size of the obstruction that casts the shadow.

59. Diffraction Features of diffraction
limitations with focusing images in optical instruments
object about the same size as wavelength of light, diffraction blurs
object smaller than wavelength of light, no image
limitations avoided with an electron beam having extremely short wavelengths

60. Diffraction Features of diffraction (continued)
electron microscopes use electric and magnetic fields to focus and magnify images
better radio reception with long radio waves
for dolphins, use of shorter wavelengths see finer detail—ultrasound

61. Interference of Light
Superposition of waves

62. Interference of Light Interference pattern
caused by interference between a pair of waves

63. Interference of Light Interference pattern (continued)
constructive interference produces bright region where waves reinforce each other (waves arriving in phase)
destructive interference produces dark region where waves cancel each other (waves arriving a half wavelength out of phase)

64. Interference of Light
Detail of interference pattern

65. The phenomenon of interference occurs for
Interference of Light
CHECK YOUR NEIGHBOR
The phenomenon of interference occurs for
A. sound waves.
light waves.
both A and B
neither A nor B
C. both of these.

66. The phenomenon of interference occurs for
Interference of Light
CHECK YOUR ANSWER
The phenomenon of interference occurs for
A. sound waves.
light waves.
both A and B
neither A nor B
Explanation:
Interference is the property that characterizes waves in general.
C. both of these.

67. Diffraction Diffraction grating
composed of a large number of close, equally spaced slits for analyzing light source
produced by spectrometers that disperse white light into colors

68. Interference Interference colors by reflection from thin films
The thin film of gasoline is just the right thickness to result in the destructive interference of blue light.

69. Interference of Light CHECK YOUR NEIGHBOR
If the thin film of gasoline was a bit thinner, the wavelength to be cancelled would be
A. shorter than that of blue.
longer than that of blue.
white.
none of the above
A. shorter than that of blue.

70. Interference of Light CHECK YOUR ANSWER
If the thin film of gasoline was a bit thinner, the wavelength to be cancelled would be
A. shorter than that of blue.
longer than that of blue.
white.
none of the above
A. shorter than that of blue.

71. Interference of Light CHECK YOUR NEIGHBOR
If violet light were cancelled by the double reflection of sunlight from gasoline on a wet surface, the resulting color would likely be
A. red.
orange.
green.
violet.
B. orange.

72. Interference of Light CHECK YOUR ANSWER
If violet light were cancelled by the double reflection of sunlight from gasoline on a wet surface, the resulting color would likely be
A. red.
orange.
green.
violet.
Explanation:
Orange is the complementary color of violet.
B. orange.

73. Interference of Light CHECK YOUR NEIGHBOR
If you see the color blue reflected in the interference from gasoline on water, and you lower your head so a greater angle from the normal results, you’ll likely see a color having a wavelength
A. shorter than that of blue.
longer than that of blue.
with a white appearance.
none of the above
A. shorter than that of blue.

74. Interference of Light CHECK YOUR ANSWER
If you see the color blue reflected in the interference from gasoline on water, and you lower your head so a greater angle from the normal results, you’ll likely see a color having a wavelength
A. shorter than that of blue.
longer than that of blue.
with a white appearance.
none of the above
Explanation:
The path through the gasoline would be longer, and a longer wavelength would be cancelled. The result of a long wave being cancelled is a shorter wave.
B. Yes for 1 and 2.

75. Interference of Light Interference colors
Note the colors in the bubble are subtractive primaries—magentas, yellows, and cyans.

76. What can the human eye not see?
Color
CHECK YOUR NEIGHBOR
What can the human eye not see?
A. infrared radiation
ultraviolet radiation
both A and B
neither A nor B
C. Both of the above.

77. What can the human eye not see?
Color
CHECK YOUR ANSWER
What can the human eye not see?
A. infrared radiation
ultraviolet radiation
both A and B
neither A nor B
C. Both of the above.