1. I. Electromagnetic Waves & Radiation
Ch. 15 Sound & Light
I. Electromagnetic Waves & Radiation
EM Waves
EM Radiation
EM Spectrum
Types of EM Radiation

2. © 2000 Microsoft Clip Gallery
LIGHT: What Is It?
Light Energy
Atoms
As atoms absorb energy, electrons jump out to a higher energy level.
Electrons release light when falling down to the lower energy level.
Photons - bundles/packets of energy released when the electrons fall.
Light: Stream of Photons
© 2000 Microsoft Clip Gallery

3. Light What is it?
Light can be modeled as a wave or as stream of particles or as rays that travel in straight lines

4. Light What is it? Photons tiny, particle-like bundles of radiation
absorbed and released by electrons
energy increases with wave frequency

5. Speed of Sound Depends on medium type and medium temperature
Speed in Vacuum
300,000,000 m/sec
186,000 mi/sec
Speed in Other Materials
Slower in Air, Water, Glass

6. Light travels much faster than sound. For example:
Thunder and lightning start at the same time, but we will see the lightning first.
2) When a starting pistol is fired we see the smoke first and then hear the bang.

7. A. EM Waves & Radiation Light waves are known as Electromagnetic Waves
Consist of changing electric and magnetic field in space

8. A. EM Waves & Radiation Electromagnetic Radiation
transverse waves produced by the motion of electrically charged particles
does not require a medium

9. Electromagnetic Spectrum
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10. B. EM Spectrum The speed of light depends on the medium
In a vacuum, light always travels at 3.0x108 m/s
Travels faster in air than in water
Fastest traveling signal in the universe

11. B. EM Spectrum The brightness of light depends on intensity
Intensity=the rate at which energy flows through a given area of space
As it spreads out, intensity decreases
A 100W light bulb is brighter than a 60W light bulb

12. B. EM Spectrum
long 
low f
low energy
short 
high f
high energy

13. C. Types of EM Radiation Radiowaves lowest energy EM radiation
Longest wavelength & Lowest frequency
Uses: Radio & TV Broadcasting

14. Modulating Radio Waves
Modulation - variation of amplitude or frequency when waves are broadcast
AM – amplitude modulation
Carries audio for T.V. Broadcasts
Longer wavelength so can bend around hills
FM – frequency modulation
Carries video for T.V. Broadcasts

15. C. Types of EM Radiation Microwaves
penetrate food and vibrate water & fat molecules to produce thermal energy

16. C. Types of EM Radiation Infrared Radiation (IR)
slightly lower energy than visible light
can raise the thermal energy of objects
Uses: cooking, medicine, TV, Remote controls
thermogram - image made by detecting IR radiation

17. C. Types of EM Radiation Visible Light
small part of the spectrum we can see
ROY G. BIV - colors in order of increasing energy R O Y G. B I V
red
orange
yellow
green
blue
indigo
violet

18. Electromagnetic Spectrum
Visible Spectrum – Light we can see
Roy G. Biv – Acronym for Red, Orange, Yellow, Green, Blue, Indigo, & Violet.
Largest to Smallest Wavelength.

19. C. Types of EM Radiation Ultraviolet Radiation (UV)
slightly higher energy than visible light
Types:
UVA - tanning, wrinkles
UVB - sunburn, cancer
UVC - most harmful, sterilization

20. C. Types of EM Radiation Ultraviolet Radiation (UV)
Ozone layer depletion = UV exposure!

21. C. Types of EM Radiation X rays higher energy than UV
can penetrate soft tissue, but not bones
Uses: medicine
Lead absorbs X-Rays

22. Radiation treatment using radioactive cobalt-60.
C. Types of EM Radiation
Gamma rays
highest energy EM radiation
emitted by radioactive atoms
used to kill cancerous cells
Radiation treatment using radioactive cobalt-60.

23. III. Wave Properties of Light
Ch. 15 – Sound & Light
III. Wave Properties of Light
Reflection
Refraction
Diffraction
Interference

24. LIGHT: Particles or Waves?
Wave Model of Light
Explains most properties of light
Particle Theory of Light
Photoelectric Effect – Photons of light produce free electrons
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25. A. Reflection Reflection when a wave strikes an object and bounces off
Normal
Reflection
when a wave strikes an object and bounces off
incident beam
reflected beam

26. A. Reflection Law of Reflection
the angle of incidence equals the angle of reflection

27. Part 2 - Reflection Reflection from a mirror: Normal
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

28. LIGHT & ITS USES: Reflection Vocabulary
Virtual Image–
“Not Real” because it cannot be projected
Image only seems to be there!

29. Light & Its Uses: Mirrors
Reflection Vocabulary
Optical Axis – Base line through the center of a mirror or lens
Focal Point – Point where reflected or refracted rays meet & image is formed
Focal Length – Distance between center of mirror/lens and focal point
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30. LIGHT & ITS USES: Mirrors
Plane Mirrors – Perfectly flat
Virtual – Image is “Not Real” because it cannot be projected
Erect – Image is right side up
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31. LIGHT & ITS USES: Mirrors
Reflection & Mirrors (Cont.)
Convex Mirror
Curves outward
Enlarges images.
Use: Rear view mirrors, store security…
CAUTION! Objects are closer than they appear!
© 2000 Microsoft Clip Gallery

32. LIGHT & ITS USES: Lenses
Convex Lenses
Thicker in the center than edges.
Lens that converges (brings together) light rays.
Forms real images and virtual images depending on position of the object

33. LIGHT & ITS USES: Lenses
Focal Point
Object
Convex Lenses
Ray Tracing
Two rays usually define an image
Ray #1: Light ray comes from top of object; travels parallel to optic axis; bends thru focal point.
© 2000 D. L. Power
Lens

34. LIGHT & ITS USES: Lenses
Ray #1
Convex Lenses
Ray Tracing
Two rays define an image
Ray 2: Light ray comes from top of object & travels through center of lens.
© 2000 D. L. Power
Ray #2

35. LIGHT & ITS USES: Lenses
© 2000 D. L. Power
Concave Lenses –
Lens that is thicker at the edges and thinner in the center.
Diverges light rays
All images are erect and reduced.

36. © 2000 Microsoft Clip Gallery © 2000 Microsoft Clip Gallery
How You See
Near Sighted – Eyeball is too long and image focuses in front of the retina
Far Sighted – Eyeball is too short so image is focused behind the retina.
© 2000 Microsoft Clip Gallery
© 2000 Microsoft Clip Gallery

37. LIGHT & USES: Lenses Concave Lenses – Vision – Eye is a convex lens.
Nearsightedness – Concave lenses expand focal lengths
Farsightedness – Convex lenses shortens the focal length.

38. LIGHT & USES: Optical Instruments
Cameras
Telescopes
Microscopes
© 2000 Microsoft Clip Gallery
© 2000 Microsoft Clip Gallery
© 2000 Microsoft Clip Gallery

39. LIGHT & USES: Optical Instruments
LASERS
Acronym: Light Amplification by Stimulated Emission of Radiation
Coherent Light – Waves are in phase so it is VERY powerful & VERY intense.

40. LIGHT & USES: Optical Instruments
LASERS
Holography – Use of Lasers to create 3-D images
Fiber Optics – Light energy transferred through long, flexible fibers of glass/plastic
Uses – Communications, medicine, t.v. transmission, data processing.

41. B. Refraction Refraction
bending of waves when passing from one medium to another
caused by a change in speed
slower (more dense)  light bends toward the normal
SLOWER
FASTER
faster (less dense)  light bends away from the normal

42. B. Refraction Refraction depends on… speed of light in the medium
wavelength of the light - shorter wavelengths (blue) bend more

43. B. Refraction
Example:
View explanation.

44. C. Diffraction Diffraction bending of waves around a barrier
longer wavelengths (red) bend more - opposite of refraction

45. D. Interference Interference constructive  brighter light
destructive  dimmer light

46. Ch. 15 – Sound & Light II. Light and Color Light and Matter
Seeing Colors
Mixing Colors

47. A. Light and Matter Opaque absorbs or reflects all light
Color you see is the color it reflects
Transparent
allows light to pass through completely
Color you see is color that is transmitted, all others are absorbed
Translucent
allows some light to pass through

48. B. Seeing Colors White light contains all visible colors - ROY G. BIV
In white light, an object…
reflects the color you see
absorbs all other colors
REFLECTS
ALL COLORS
ABSORBS
ALL COLORS

49. Stimulates red & green cones
B. Seeing Colors
The Retina:
Lens refracts light to converge on the retina. Nerves transmit the image
The retina contains…
Rods - dim light, black & white
Cones - color
red - absorb red & yellow
green - absorb yellow & green
blue - absorb blue & violet
Stimulates red & green cones
Stimulates all cones

50. Test for red-green color blindness.
B. Seeing Colors
Test for red-green color blindness.
Color Blindness
one or more sets of cones does not function properly

51. View Java Applet on primary light colors.
C. Mixing Colors
Primary light colors
red, green, blue
additive colors
combine to form white light
EX: computer RGBs
View Java Applet on primary light colors.

52. Seeing colour Homework
The colour an object appears depends on the colours of light it reflects.
For example, a red book only reflects red light:
Homework
White
light
Only red light is reflected

53. A white hat would reflect all seven colours:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colours:
White
light

54. View Java Applet on filters.
C. Mixing Colors
Filter
transparent material that absorbs all light colors except the filter color
View Java Applet on filters.

55. Using filters
Filters can be used to “block” out different colours of light:
Red Filter
Magenta Filter

56. C. Mixing Colors Pigment
colored material that absorbs and reflects different colors
Primary pigment colors
cyan, magenta, yellow
subtractive colors
combine to form black
EX: color ink cartridges

57. C. Mixing Colors Light: RGB Pigment: CMYK
When mixing pigments, the color of the mixture is the color of light that both pigments reflect.

58. C. Mixing Colors RGB (light colors) Red + Green= Yellow
Red + Blue = Magenta
Green + Blue = Cyan
R+G+ B = White
No light = Black
What ever you need to mix gets reflected, whatever you don’t need gets absorbed
Example: Cyan Reflects blue and green, Absorbs Red

59. C. Mixing Colors CMYK (pigment colors) C+M=blue C+Y=green M+Y=red
C+M+Y= Black (K)
No Pigment= white
What ever you need to mix gets reflected, whatever you don’t need gets absorbed
Example: Green reflects cyan and yellow; absorbs magenta

61. Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.

62. © 2000 Microsoft Clip Gallery © 2000 Microsoft Clip Gallery
LIGHT & ITS USES
© 2000 Microsoft Clip Gallery
Sources of Light
Incandescent light – light produced by heating an object until it glows.
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63. © 2000 Microsoft Clip Gallery
LIGHT & ITS USES
© 2000 Microsoft Clip Gallery
Fluorescent Light –
Light produced by electron bombardment of gas molecules
Phosphors absorb photons that are created when mercury gas gets zapped with electrons. The phosphors glow & produce light.

64. © 2000 Microsoft Clip Gallery
LIGHT & ITS USES - Neon
Neon light – neon inside glass tubes makes red light. Other gases make other colors.
© 2000 Microsoft Clip Gallery

65. E. Cool Applications! Fiber Optics Total Internal Reflection
when all light is reflected back into the denser medium

66. E. Cool Applications! The “Broken Pencil” refraction
View animation and explanation of the “Broken Pencil.”

67. E. Cool Applications!
Rainbows
refraction-reflection-refraction

68. E. Cool Applications! Diffraction Gratings
glass or plastic made up of many tiny parallel slits
may also be reflective
spectroscopes, reflective rainbow stickers, CD surfaces

69. E. Cool Applications! Thin Films - Bubbles & Oil Slicks
interference results from double reflection

70. E. Cool Applications! Blue Sky & Red Sunsets
Molecules in atmosphere scatter light rays.
NOON
less atmosphere
less scattering
blue sky, yellow sun
Shorter wavelengths (blue, violet) are scattered more easily.
SUNSET
more atmosphere
more scattering
orange-red sky & sun