1. Waves: light and sound

2. Inquiry activity Light lab: variety of stations
Stations 1, 8, and 9 : HW
Stations 2, 3, 4, and 5: one class period

3. Synopsis of light lab stations
1. internet
2. 1 flat mirror & laser
3. 2 flat mirrors & laser
4. concave mirror & laser
5. convex mirror & laser
6. carpet and wheels
7. mug with water
8. internet
9. phet wave interference
10. CDs and DVDs & lasers

4. Light labs Move through quickly!! Groups of 3 at the most
Important to draw accurate diagrams for incoming and outgoing rays!
After we review the results as a class, I will post expected answers ONLINE.

5. Why did we use lasers? Why do we talk about rays of light?
Curved wavefronts like ripples on a pond travel out in all directions….far enough away looks like a flat wavefront.
A ray shows the direction that wave is travelling; easier to draw.
Useful for modelling behavior of light

6. To study properties of light, simplify light into rays
Although light travels in all directions and hits all surfaces from all directions, it is useful to
Think of light travelling as parallel rays

7. Station 1: All about Waves
Answers in separate document

8. Light lab emphasized characteristics that describe all waves
Station1 introduced:
Crest and trough
Amplitude
Wavelength
Frequency in Hertz (cycles/sec)
Speed of a wave

9. Waveform – A Picture of a Wave
The brown curve is a “snapshot” of the wave at some instant in time
The blue curve is later in time
The high points are crests of the wave
The low points are troughs of the wave

10. Amplitude and Wavelength
Amplitude is the maximum displacement of string above the equilibrium position
Wavelength, λ, is the distance between two successive points that behave identically

11. Speed of a Wave
v = ƒ λ
derived from the basic speed equation of distance/time
a general equation that can be applied to many types of waves
Speed of light = assumed constant
variable ‘c’, for ‘celeritas’, Latin for swiftness
approx 3 x 108 m/s in a vacuum
slows down slightly while passing through glass, etc.
Speed of sound, water, etc. depends on many variables

12. Light lab also introduced some properties and behavior of waves
What do waves do?
transmit energy
can be reflected (stations 2, 3, 4, 5)
can interfere with each other (stations 8, 9)

13. Station 2: Reflect on this
Flat mirror and laser
Results: angle of incoming ray is equal to outgoing ray, if measured from a line perpendicular to the mirror

14. Station 2: Law of Reflection
The normal is a line perpendicular to the surface
The incident (incoming) ray makes an angle of θ1 with the normal
The reflected (outgoing) ray makes an angle of θ1’ with the normal
The angle of reflection is equal to the angle of incidence
θ1= θ1

15. Law of Reflection, cont
This is true for all types and shapes of reflecting surfaces
Why do you see a reflection on some surfaces and not on others???

16. Station 3: Target Practice
Rays follow law of reflection
Conclusion: incoming and outgoing rays are parallel to each other no matter what the orientation of the incoming
Caveat: incoming ray must reflect off both mirrors

17. Big Idea Without light there can be no sight! What does that mean?
The only way we can
See objects is
Because they…

18. We see objects that reflect light back into our eyes!!!
No light at all, can’t see the object
No direct path of reflected light, can’t see it
A blockage in the path, can’t see it

19. Prisms can be also used like mirrors (more on prisms later)

20. Station 4: Why..look funny? Pt1
Working with CONCAVE mirrors
Answers also available in separate word document on my website

21. Ray Diagram for Concave Mirror, p > R
The object is outside the center of curvature of the mirror
The image is inverted
The image is smaller than the object

22. Ray Diagram for a Concave Mirror, p < f
The object is between the mirror and the focal point
The image is upright
The image is larger than the object

23. Focal Length Shown by Parallel Rays

24. Station 5: Why…so funny? Pt2
Working with CONVEX mirrors
Answers also available in separate word document on my website

25. Image Formed by a Convex Mirror

26. Convex Mirrors sometimes called a diverging mirror
The rays from any point on the object diverge after reflection as though they were coming from some point behind the mirror
The image is virtual because it lies behind the mirror at the point where the reflected rays appear to originate

27. Ray Diagram for a Convex Mirror
The object is in front of a convex mirror
The image is upright
The image is smaller than the object

28. Spherical Mirrors
A spherical mirror has the shape of a segment of a sphere
A concave spherical mirror has the silvered surface of the mirror on the inner, or concave, side of the curve
A convex spherical mirror has the silvered surface of the mirror on the outer, or convex, side of the curve

29. Specific data about non-flat mirrors
The mirror has a radius of curvature of R
Its center of curvature is the point C
Point V is the center of the spherical segment
A line drawn from C to V is called the principal axis of the mirror

30. Station 8:Interference of Waves
Two traveling waves can meet and pass through each other without being destroyed or even altered
Waves obey the Superposition Principle
If two or more traveling waves are moving through a medium, the resulting wave is found by adding together the displacements of the individual waves point by point
Actually only true for waves with small amplitudes

31. Constructive Interference
Two waves, a and b, have the same frequency and amplitude
Are in phase
The combined wave, c, has the same frequency and a greater amplitude

32. Destructive Interference
Two waves, a and b, have the same amplitude and frequency
They are 180° out of phase
When they combine, the waveforms cancel

33. Station 9: It all adds up Phet website wave interference
Use 2 sources of water,
Sound, light waves

34. Interference Constructive interference Destructive Nodes or
areas of zero
amplitude

35. Other activities will explore additional wave properties such as
can be refracted or bent when hittingboundary or edge
Under the right circumstances they can form harmonious patterns on a string
‘white’ Light can be split into various wavelengths, colors

36. Get back to basics: What are waves?
Waves are a transmission of energy
Many waves travel through matter such as
Waves through water
Sound through air, water, walls, etc.
Earthquake waves through the earth
Some waves travel do not require matter such as electro-magnetic waves

37. EQ and sound waves

38. Light is an e-m wave Many thanks to Faraday and Maxwell!!
Behavior of light can
be described using
the previous vocab
Also has unique behaviors and properties

39. Einstein kept pictures of Maxwell and Newton in his room

40. Types of Waves – Traveling Waves and standing waves
Travelling wave
Any wave that is free to travel , not confined such as
Earthquake waves
Waves on ocean
Sound
E-m radiation
Light
Standing wave
Resonance in solids
Standing wave on musical instrument
Standing wave on any string or coil
Tacoma Narrows bridge
Resonance in a air column
Standing pressure wave in musical instrument
Resonating bodies

41. Types of Waves – Transverse
In a transverse wave, each element that is disturbed moves in a direction perpendicular to the wave motion
Examples: e-m, light, water, waves on string

42. Types of Waves – Longitudinal
In a longitudinal wave, the elements of the medium undergo displacements parallel to the motion of the wave
A longitudinal wave is also called a compression wave
Sound is a compression/longitudinal wave

43. Longitudinal Wave Represented as a Sine Curve
A longitudinal wave can also be represented as a sine curve
Compressions correspond to crests and stretches correspond to troughs
Also called density waves or pressure waves

44. Stations 6, 7 Wheels, carpeted or smooth surface Mug, coin and water
REFRACTION IS THE MESSAGE!

46. IS THE OBJECT YOU SEE REALLY WHERE YOU THINK IT IS??
If you are trying to spear a fish, where should you aim??
Closer to you or farther away?

47. Aim closer!! You are fooled into thinking the light is coming in a
straight line to your eye.
The fish is closer than you think

48. Following the Reflected and Refracted Rays
Ray  is the incident ray
Ray  is the reflected ray
Ray  is refracted into the lucite
Ray  is internally reflected in the lucite
Ray  is refracted as it enters the air from the lucite

49. Refraction of Light
When a ray of light traveling through a transparent medium encounters a boundary leading into another transparent medium, part of the ray is reflected and part of the ray enters the second medium
The ray that enters the second medium is bent at the boundary
This bending of the ray is called refraction

50. Refraction of Light, cont
The incident ray, the reflected ray, the refracted ray, and the normal all lie on the same plane
The angle of refraction, θ2, depends on the properties of the medium

51. Refraction in a Prism
The amount the ray is bent away from its original direction is called the angle of deviation, δ
Since all the colors have different angles of deviation, they will spread out into a spectrum
Violet deviates the most
Red deviates the least

52. Explaining the mysteries of nature with physics!!
If a raindrop high in the sky is observed, the red ray is seen
A drop lower in the sky would direct violet light to the observer
The other colors of the spectra lie in between the red and the violet

53. Explaining nature’s rainbows pt2
At the back surface the light is reflected
It is refracted again as it returns to the front surface and moves into the air
The rays leave the drop at various angles
The angle between the white light and the violet ray is 40°
The angle between the white light and the red ray is 42°

54. Total Internal Reflection: like aiming a pebble at just the right angle so it skips off the water
Total internal reflection can occur when light attempts to move from a medium with a high index of refraction to one with a lower index of refraction
Ray 5 shows internal reflection

55. CD vs DVD See ppt on ‘applications’
See Word document on ‘light stations’

56. Sound as a wave

57. Producing a Sound Wave
Sound waves are longitudinal waves traveling through a medium
A tuning fork can be used as an example of producing a sound wave

58. Using a Tuning Fork to Produce a Sound Wave
A tuning fork will produce a pure musical note
As the tines vibrate, they disturb the air near them
As the tine swings to the right, it forces the air molecules near it closer together
This produces a high density area in the air
This is an area of compression

59. Using a Tuning Fork, cont.
As the tine moves toward the left, the air molecules to the right of the tine spread out
This produces an area of low density
This area is called a rarefaction

60. Using a Tuning Fork, final
As the tuning fork continues to vibrate, a succession of compressions and rarefactions spread out from the fork
A sinusoidal curve can be used to represent the longitudinal wave
Crests correspond to compressions and troughs to rarefactions

61. Speed of Sound Speed is higher in solids than in gases
The molecules in a solid interact more strongly
Can you use this info to hear better?
Old mechanic’s trick of putting one end of a wrench against forehead and other against part of engine to ‘listen’ for source of engine noise
Try different spots on engine
Noise will be loudest at one spot

63. Categories of Sound Waves
Audible waves
Lay within the normal range of hearing of the human ear
Normally between 20 Hz to 20,000 Hz
Infrasonic waves
Frequencies are below the audible range
Earthquakes are an example
Ultrasonic waves
Frequencies are above the audible range
Dog whistles are an example

65. Intensity of Sound, I Threshold of hearing Threshold of pain
Faintest sound most humans can hear
About 1 x W/m2
Threshold of pain
Loudest sound most humans can tolerate
About 1 W/m2
The ear is a very sensitive detector of sound waves
It can detect pressure fluctuations as small as about 3 parts in 1010

66. What are decibels?
β is the intensity level or the decibel level of the sound compared to the human threshold of hearing
Io is the threshold of hearing

67. Various Intensity Levels
Threshold of hearing is 0 dB
Threshold of pain is 120 dB
Jet airplanes are about 150 dB
Table 14.2 lists intensity levels of various sounds
Multiplying a given intensity by 10 adds 10 dB to the intensity level

68. Frequency Response Curves
Bottom curve is the threshold of hearing
Threshold of hearing is strongly dependent on frequency
Easiest frequency to hear is about 3300 Hz
When the sound is loud (top curve, threshold of pain) all frequencies can be heard equally well

69. What can you normally hear? What defines hearing loss?

70. What, if anything, can ‘old people’ hear?
Can’t hear high frequencies, 14,000 Hz max
Not bad if you look at the previous graph
Take a hearing test
Is this normal aging process useful info?
It’s the basis for ‘The Mosquito’!

71. The Mosquito… innovation driven by need

72. Sound and NASCAR Why do the cars sound funny when they go by?
In Sheldon’s words…

73. Doppler Effect Commonly experienced with sound waves,
But common to all waves
Usually experienced with
listener being stationary and
source in motion

74. Source in Motion
As the source moves toward the observer (A), the wavelength appears shorter and the frequency increases
car moving toward him sounds high pitched
As the source moves away from the observer (B), the wavelength appears longer and the frequency appears to be lower
Car moving away from her sounds lower pitched

75. Doppler effect: stars

76. Bats Radar gun

77. Applications of Ultrasound
Can be used to produce images of small objects
Widely used as a diagnostic and treatment tool in medicine
Ultrasonic flow meter to measure blood flow
May use piezoelectric devices that transform electrical energy into mechanical energy
Reversible: mechanical to electrical
Ultrasounds to observe babies in the womb
Cavitron Ultrasonic Surgical Aspirator (CUSA) used to surgically remove brain tumors
Ultrasonic ranging unit for cameras

78. When object is moving so fast it is ‘catching’ up with the sound waves it’s producing….
Shock waves carry energy concentrated on the surface of the cone, with correspondingly great pressure variations
A jet produces a shock wave seen as a fog

79. Interference of Sound Waves
Sound waves interfere
Constructive interference
Destructive interference
Example of concert halls, auditioriums
Sound is produced on stage
Reflected by walls, etc
Can be absorbed by curtains, seats, etc.
Can be transmitted through walls, etc.
Acoustic design is extremely important to performers and to the audience

80. Sound and Musical Instruments
String
Brass
Woodwinds
Percussion

81. Let’s compare
Tuning fork C at 256 ?
Instrument’s C…

82. Compare instruments.. How is sound created on each instrument?
What is the same? What is different?
Why does C sound different on each?

83. Forced Vibrations
A system with a driving force will force a vibration at its frequency
When the frequency of the driving force equals the natural frequency of the system, the system is said to be in resonance

84. An Example of Resonance
Pendulum A is set in motion
The others begin to vibrate due to the vibrations in the flexible beam
Pendulum C oscillates at the greatest amplitude since its length, and therefore frequency, matches that of A

85. Other Examples of Resonance
Child being pushed on a swing
Shattering glasses
Tacoma Narrows Bridge collapse due to oscillations by the wind
Upper deck of the Nimitz Freeway collapse due to the Loma Prieta earthquake

86. Stringed instruments Vibration started with force applied to string
Various lengths and thicknesses of strings
Various tensions on the strings

87. Standing Waves on a String
Nodes must occur at the ends of the string because these points are fixed

88. Standing Waves on a String, final
The lowest frequency of
vibration (b) is called
the fundamental frequency
Affected by:
F, tension of string,
L, length of vibrating portion of string,
Mass/unit length of the string

89. Standing Waves on a String – Frequencies
ƒ1, ƒ2, ƒ3 form a harmonic series
ƒ1 is the fundamental and also the first harmonic
ƒ2 is the second harmonic
Waves in the string that are not in the harmonic series are quickly damped out
When the string is disturbed,
it “selects” the standing wave frequencies

90. Compare the equation variable to the different parts of the instrument
How can these be varied
Tension
Length of string vibrating
Mass/unit length of string?
Violin, viola, cello, bass, harp, piano…
What is the function of the body of the instrument?

91. Brass Air goes in one end and out the other
Vibration starts with musician’s lips
Valves are used to alter the total length of the pipe

92. Woodwind Air goes in one end and out at many places
Generally ‘open ended’
Vibration starts with air passing over a reed
Keys are used to alter the length of the vibrating column

93. Standing Waves in Air Columns
If one end of the air column is closed, a node must exist at this end since the movement of the air is restricted
If the end is open, the elements of the air have complete freedom of movement and an antinode exists

94. Tube Open at Both Ends

95. Resonance in Air Column Open at Both Ends
In a pipe open at both ends, the natural frequency of vibration forms a series whose harmonics are equal to integral multiples of the fundamental frequency

96. How do you create different notes?

97. Tube Closed at One End, pipe organ, or bottle or glass

98. Resonance in an Air Column Closed at One End
The closed end must be a node
The open end is an antinode
There are no even multiples of the fundamental harmonic
V velocity of air
L length of air column

99. Pitch
Pitch is related mainly, although not completely, to the frequency of the sound
Pitch is not a physical property of the sound
Frequency is the stimulus and pitch is the response
It is a psychological reaction that allows humans to place the sound on a scale

100. Timbre
In music, the characteristic sound of any instrument is referred to as the quality of sound, or the timbre, of the sound
The quality depends on the mixture of harmonics in the sound

101. Quality of Sound – Tuning Fork
Tuning fork produces only the fundamental frequency

102. Quality of Sound – Flute
The same note played on a flute sounds differently
The second harmonic is very strong
The fourth harmonic is close in strength to the first

103. Quality of Sound – Clarinet
The fifth harmonic is very strong
The first and fourth harmonics are very similar, with the third being close to them

104. Loudness Loudness = amplitude of sound wave
Generally measured in decibels

105. Beats Beats are alternations in loudness, due to interference
Waves have slightly different frequencies and the time between constructive and destructive interference alternates
The beat frequency equals the difference in frequency between the two sources:

106. The Ear
The outer ear consists of the ear canal that terminates at the eardrum
Just behind the eardrum is the middle ear
The bones in the middle ear transmit sounds to the inner ear

108. Light lab also introduced some properties and behavior of waves
What do waves do?
transmit energy
can be reflected
can be refracted or bent when they hit a boundary or edge
can interfere with each other
Under the right circumstances they can form harmonious patterns on a string
They can pass through some materials better than others