Waves and Sound Review
Name _ _ _ _ _ _ _ _ _ _ __
Waves-General
Vocabulary: crest, trough, wavelength, period, fi'equency, pitch, amplitude, node, anti-node, transverse wave,
longitudinal wave, standing wave, compression, rarefaction, infrasonic, ultrasonic, resonance, harmonics,
Doppler Effect, red shift, shock wave, constructive interference, destructive interference
Frequency (I) = # waves/time (unit = IIsec = hertz)
Period (T) = time for one wave cycle (unit = seconds)
Types of waves:
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Transverse: water waves, S-waves in em1hquakes
Longitudinal: sound waves, P-waves in earthquakes
Law of Snperposition: During interference, the amplitudes of2 or more waves add together
Constrnctive Interference: crests add to crests, and troughs add to troughs, increasing the amplitude
Destructive Interference: crests add to troughs, decreasing the amplitude
Energy of a wave: amplitude measures the amount of energy in a wave
Wave Speed = wavelength x frequency (unit = m/sec)
velocity = i1p/i1t (distance traveled/travel time) (unit = m/sec).
Denser media = faster wave speed
Tension: increasing the tension in a medium will increase the wave speed (i.e. guitar string)
Standing Waves: created when incident and reflected waves interfere to make stable patterns of constructive
and destructive interference. The higher the fi'equency, the more nodes will be created (shorter wavelength)
In strings: Nodes must be located at the end points.
In tubes: displacement anti-nodes will be at open ends of the tube, nodes will be at closed ends.
Speed of waves in various media
• Waves need a medium.
• Waves travel at a measurable speed (speed is fixed for a specific medium).
• Waves travel fastest and best (lose less energy) through denser media
Doppler Effect: the change in frequency caused by moving wave source or an observer moving relative to a
wave source. The fi'equency of a wave is increased in front of a moving wave source, and decreased behind
the wave source.
Example: The sound ofa car engine passing you sounds higher as it approaches you, and lower as·it moves
away fi'om you. The actual pitch of the car engine is in between the high and low pitch (you hear this pitch
for the very brieftime that the car is right alongside you).
Sound Waves
Sound -- General
• Sound sources are vibrating objects.
• Standing waves create continuous sounds (vibrating tuning fork, wine glass, etc)
• Sound travels away from source.
• Sound waves are longitudinal waves and create a series of compressions and rarefactions (expansions)
• The size and properties of the vibrating object affect the sound produced.
• While sound is a longitudinal wave, it's often represented as a transverse wave because it's easier to draw.
• Our perception of sound is related to the sound waves properties: frequency - pitch, amplitude - loudness,
complexity - quality/tone
Frequ ency and Pitch
• T he faster the frequency, the lower the wave length, the hi gher the pi tc h.
• T he frequency created by an obj ect depends on that objects compos ition, de nsity, tens ion, and length.
• T he pitch of a sound can be mani pulated us ing the things listed above. Mus ic.is made this way.
• Notes on in struments are created by standin g waves in the obj ect produc in g the sound .
Resonance and Harmonics
• Everything has a natural vibrating frequ ency . Somethin g vibrating at thi s freq uency has resonance.
• Obj ects can al so have forced vibrations. (tuning fork makin g a table to p v ibrate w ith the same frequency)
• T he amplitude o f an object's vibrati ons can be increased if the vibrations o f another obj ect matches the
natura l frequency o f the first obj ect. Exampl es : Tuning forks of the same note, Tacoma Narrows Bridge, a
boy bounc ing a ball , a child be ing pushed on a sw ing, a s inger shattering a g lass .
• Standi ng waves w ith increasing numbers of nodes create harmonics in a vibrating obj ect.
Pra ctice Problems:
I. Draw a transverse wave and labe l: Wavelength, amplitude, crest, tro ugh.
2 . Draw a spring pul se mov ing towa rd a fi xed end then draw the re fl ected pul se as it travels back. (i nclude
d irection arrows) .
Pulse Toward F ixed end
Reflected pulse
4. The transverse wave below represents the air pressure of a (long itudina l) sound wave traveling in the air. .
Use it to answer the following questions: (in all cases, assume the same medium)
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c. Dra2 awave that had the same pitch but was softer:
d. Draw a wave that wo uld have a higher pitch:
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e. Which of the waves that you drew has the longest wavelength (a, b, c, d)? _ _ __
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Wh ich of the waves you drew has the highest frequency?
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f. Whi ch of the waves you drew wou ld trave l the s lowest?
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5. Describe two situations where resonance can be observed.
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6. Explain with a sketch why an ambulance siren sounds higher pitched when approachi ng you and lower
pitched when moving away from you.
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8. Describe th ree different ways that pitch can be maniR,;ilated in a guitar to make music.
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9. Guitars and pianos are both stringed in strum ents. Why do they sound so di fferent?
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10. Draw the fundamental and second and third harmonics of a standing wave mov ing between the endpoi nts
shown below. Wh ich note wi ll have the lowest pitch ? Wh ich 2 notes will be octaves? Label the nodes,
anti-nodes, amplitude and wavelength for the third harm onic.
Second Harmonic:
Fundamental:
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Th ird Harmonic:
II. Why do longer objects make lower-pitched notes than short objects?
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12. The speed of so und in fresh water at 20°C is 1482 m/sec, whil e it is 1522 m/sec in seawater at 20°C. Why
do you think it is faste r in seawater?
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13. Two bottlenose dolphins are carry in g on a long distance co nversat ion. If they are 200 km apart, and the
speed of sound in seawater is 1.522 km/sec, how long will it take one dolphin to hear the oth er?
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14. The bott le nose dolphin s are communicating at a frequ ency of 100,000 Hz. What is the wavelength of
these waves in seawater (v = 1522 m/sec)?
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IS. If a girl is bouncing a ball with a frequency of2 bounces/seco nd , what isthe period of bouncing?
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Name: _______________________________
Period:
Waves Extra Practice
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3. Label the picture below with: rarefaction, compression, wavelength
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4. In the standing wave pictured be low, label: Antinode, Node
5. Describe what creates a standing wave:
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Which of t hese is not related to frequency?
A. amplitude
B. wavelength
-IL- 7. Which of these affects wave speed?
A. the tension of a spring.
B. the density of the medium.
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8. Sound trave ls fastest in
A. gases.
B. liquids.
C. The type of medium it travels in
D. All the above
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~ 9. To increase the number of anti-nodes in a standing wave,
A. the frequency must be increased.
B. the wavelength must be increased.
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C. the amplitude must be increased.
D. all of the above .
10. The amplitude of a longitudina l wave is measured by
A.. the amount of medium displaced by the waves.
B. the height of a compression wave.
C. the distance between compressions.
D. the amount of compression in the waves
L 11.
If the frequency of a wave was doubled from its original va lue (in the same medium), the
A. wavelength would be doubled.
C. amplitude would decrease.
B. wavelength would be halved
D. amplitude would increase.
12. Use the pictures below to draw what would happen at the point of interference.
A.
Draw the interference be low
B.
Draw the interference below
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13. Which wavers) above (A, B) will destructively interfere?
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A. bounce off each other.
C. continue to affect each other.
B. pass through each other.
D. none of the above .
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What do waves transfer?
A. material
B. energy
C. A and B
D. waves do not transfer anything.
Light, etcetera
I) What is wavi ng in a light wave?
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2) Is li g t ran sver e r longitudinal?
3) Which has a longer wave length (in the sa me med ium) red li gl or x-rays?
4) Wh ich has a lower frequency (in the same med ium ): ultravi olet li ght 0 mi crowaves.
5) What is fi ssion?
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s~I(e.-6) Where does fusion occur?
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7) Why won' t the sun become a black hole?
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