Name (printed) _______________________________
READING, QUESTIONS, AND PROBLEMS
INTRODUCTION TO WAVES
First Day Stamp
Read Sections 11-7, 11-8, and 11-9 (first two paragraphs only). Use these sections to answer the following questions:
1.
What is a wave?
2.
What is the difference between a transverse and a longitudinal wave?
3.
What is the difference between the wavelength of a wave and its amplitude?
4.
What is the difference between the period of a wave and its frequency?
5.
What feature of a wave is related to the energy content of the wave and what is that relationship?
6.
What equation relates the period of a wave to its frequency?
7.
What is the equation that relates the wavelength of a wave, its frequency, and its speed?
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For credit, you must provide a clear and complete explanation for each of the following questions.
8. _____
9. _____
If the amplitude of a wave doubles, its energy increases by a factor of
a. 1.4
b. 1.7
c. 2
d. 4
Consider the waves coming from the ocean to the beach. If the wave period increases, the number of
waves reaching the beach in one minute will
a. increase
b. decrease
c. remain the same
d. can’t be determined
10. _____ The speed of light is 3.0 x 108 m/s. The frequency of light whose wavelength is 5.0 x 10-7 m is
b. 6.0 x 1015 Hz
c. 1.7 x 1014 Hz
d. 1.7 x 1015 Hz
a. 6.0 x 1014 Hz
11. _____ A tuning fork has a frequency of 524 Hz. If the speed of the sound is 344 m/sec, what is the approximate
wavelength of the sound?
a. 0.657 m
b. 1.52 m
c. 180 m
d. 1.80 x 105 m
12. _____ Calculate the wavelength of a sound wave with a speed of 330 m/s and a period of 4 10 0 s.
d. 1.32 x 105 m
a. 0.825 m
b. 1.21 m
c. 7.58 x 10-6 m
13. _____ A string fixed at both ends as shown in the diagram to the right is set
into a standing wave vibration. If the frequency of vibration is 340 Hz,
what is the speed of the waves in this string?
a. 340 m/s
c. 1020 m/s
e. 2040 m/s
b. 680 m/s
d. 1360 m/s
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LABETTE
INTRODUCTION TO WAVES
PURPOSE
• To determine what factors affect wave velocity.
• To determine the effects of “open” and “closed” end reflections on waves.
• To determine the effect of collisions on colliding waves.
PROCEDURE
I. DETERMINING THE FACTORS THAT AFFECT WAVE VELOCITY
1.
2.
3.
Stretch the slinky out on the floor to a length of 15 feet. Count the floor tiles, which are each a square foot.
Hold each end of the slinky firmly to the floor.
CAUTION: Avoid releasing an end of the stretched spring; the untangling process can be very
difficult. Slinkys cost $15 and you WILL be charged.
With one end held rigidly in place, give the other end a quick, sharp jerk to the side and then bring it back
immediately to its starting position. The pulse generated must have a well-defined beginning and end for
your observations to be meaningful. This type of wave pulse is called transverse. Why?
Use the stopwatch to measure transverse wave speed. The timing will be rather short, and human reaction
time will greatly affect your measurements, so develop a system to avoid human reaction time. Calculate
the average time, and then the speed in feet per second using v = d/t.
Trial 1
Trial 2
Trial 3
transverse
wave time
slinky length: ________
4.
transverse wave speed: ________
Repeat step 3 with the Slinky stretched to 20 feet. (It is important to note her that changing the length of the
slinky changes the medium of the spring). DO NOT go beyond this length because the Slinky will be
damaged! Important: Stretching the slinky to a longer length is changing the medium of the slinky.
Again, measure the transverse wave speed in feet per second.
Trial 1
Trial 2
Trial 3
transverse
wave time
slinky length: ________
1. _____
transverse wave speed: ________
When the spring’s length is increased, the speed of the pulse
a. increases.
b. stays the same.
c. decreases.
Now generate two pulses of different sizes to see if they travel at the same or different speeds. Generate the two
pulses, one immediately after the other. Look to see if the rear pulse catches up with the front pulse, gets further
behind, or stays the same distance behind?
2. _____
When the size and shape of the pulse is changed, the speed of the pulse
a. changes.
b. stays the same.
3
Make a statement about what you have found determines the speed of a wave (in general, not just for slinkies).
Explain why this is important for the audience of listeners at a concert that has both loud and soft instruments that
play both high-pitched and low-pitched sound waves.
II. DETERMINING THE EFFECT OF REFLECTION ON THE WAVE
With the spring stretched to 20 feet, have your partner hold the far end of the slinky firmly against the floor.
Create a sharp, single well-defined pulse. This type of reflection is called a “closed end” reflection. Now have your
partner hold the very end of the string. Create a sharp, single well-defined pulse. This type of reflection is called
an “open end” reflection.
3. _____
What is the orientation of the reflected pulse when the end is held in place by your hand (closed end)?
a. same side of spring
b. inverted (other side of spring)
4. _____
What is the orientation of the reflected pulse when the end can move back and forth at the end of the
piece of string (open end)?
a. same side of spring
b. inverted
You should have noticed that the reflections in both cases had the same basic shape, but that the amplitudes were
smaller after the reflection. Make a statement about how each of these observations relates to sound wave echoes.
“Same basic shape:”
“Smaller amplitude:”
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III. DETERMINING THE EFFECT OF WAVE PULSE “COLLISIONS”
You and your partner should generate pulses of different sizes from each end of the spring at the same time.
Observe what happens when the two pulses meet.
5. _____
When two pulses travel in the same spring from opposite ends they
a. bounce off each other
b. pass through each other
c. destroy each other
6. _____
Again generate two pulses traveling toward each other. Have the two
pulses on the same side of the spring as shown to the right. The amplitude
of the pulse is the distance from the top of the pulse to the rest position of
the spring. When two pulses are produced on the same side of the spring
from opposite ends and they meet in the middle, the resulting amplitude is
a. zero.
c. average of the two.
b. less than either pulse.
d. greater than either pulse.
7. _____
You probably won’t be able to actually see this, but perhaps you can
hypothesize about two pulses of equal amplitude being produced on
opposite sides of the spring from opposite ends, as shown to the right.
When they meet in the middle, the resulting amplitude is
a. zero.
b. greater than either pulse.
Use questions 5 and 6 to explain both how you can hear individual conversations at a party attended by multiple
people even when they occur together in the same room and also why the loudness of the combined conversations
is greater than the loudness of an individual conversation.
From #5:
From #6:
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QUESTIONS AND PROBLEMS
INTRODUCTION TO WAVES
1.
The pulse shown below is going into a more rigid medium. Draw the reflected and transmitted pulses in the
empty spaces provided.
Before
More rigid
After
2.
Let’s say the wave to the below represents the sound wave from a 440 Hz tuning fork. On the line below, draw
the shape of the wave coming from a quieter 880 Hz tuning fork. (There are two changes here.)
For credit, you must provide a clear and complete explanation for each of the following questions.
A hint for answering each of these is that the medium for the sound wave (which is the air around the tuning fork) is
not changing
3. _____
A 440 Hz tuning fork is struck and the wave has a particular wavelength. What would happen to the
wavelength of the sound wave if a tuning fork with a higher frequency than 440 Hz were used?
a. increase
b. decrease
c. remain the same
4. _____
A 440 Hz tuning fork is struck and the wave has a particular period. What would happen to the period of
the sound wave if a tuning fork with a higher frequency than 440 Hz were used?
a. increase
b. decrease
c. remain the same
5. _____
A 440 Hz tuning fork is struck and the wave has a particular speed. What would happen to the speed of
the sound wave if a tuning fork with a higher frequency than 440 Hz were used?
a. increase
b. decrease
c. remain the same
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6.
In each of the following two cases, the wave pulses are moving toward each other. Assume that each wave
pulse moves one graph grid for each new graph. Draw the shape the medium would have in each of the blank
graphs below.
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QUESTIONS AND PROBLEMS
INTRODUCTION TO SOUND
1.
The temperature is -20°C. What is the speed of sound?
2.
An ultrasonic sound wave has a frequency of 45,000 Hz and a speed in air of 342 m/s. What is the air
temperature?
3.
What is the ratio of the speed of sound in air at 0° C to the speed at 100° C?
4.
You’re in the alps (where the air temperature is 10°C) and want to try your yodeling skills. You give a holler
toward a cliff 515 m away and wait for the echo to return. How long do you have to wait?
5.
The Ocular Hypertension Treatment Study (OHTS) a few years ago found a link between corneal thickness
and the probability of getting glaucoma. Many optometrists now use a ultrasound device to calculate the
thickness of the cornea. The device produces sound waves that move at 1500 m/s from the front surface of the
cornea to the back surface and then reflect back. The device uses the amount of time for the echo of the sound
waves to return to calculate the thickness of the cornea. If the time for the echo to return in a particular patient
is 8.0 x 10-7 s, what is the thickness of the cornea?
6.
Fish finders on boats produce sound waves that can reflect off schools of fish. If a school of fish is 50 meters
below a boat, how quickly will the echo of a fish finder return after the sound pulse is made (assume 1500 m/s
for the speed of sound in water)?
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7.
How many times louder is 79 dB sound than a 73 dB sound?
8.
What is the number of decibels that is 16 times louder than 84 dB?
9.
What is the decibel level of a sound that is 20 times quieter than 95 dB?
10.
How many times louder is 90 dB sound than a 64 dB sound?
11.
What is the decibel level of a sound that is 16,000 times quieter than 86 dB?
12.
What is the decibel level of the sound that is 2,000 times quieter than 12 dB
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QUESTIONS AND PROBLEMS
THE DOPPLER EFFECT
1.
A woman who doesn’t appreciate the improper advances of a rude thug blasts him with some pepper spray. She
then screams that her next move will be to give him a little “lead poisoning” from her licensed firearm, which
she lovingly refers to as “my li’l equalizer.” The frequency of her scream is a piercing 1,000 Hz on an evening
when the air temperature is a brisk 10°C. If the thug starts sprinting away from the woman at a speed of 7 m/s,
what frequency will he hear? 979 Hz
2.
The thug didn’t run fast enough and ... he’s down for the count. You happen to be in the area driving at a speed
of 25 m/s when the ambulance, called to remove his riddled remains, approaches from behind at 45 m/s and
with a siren frequency of 1,400 Hz. El Niño has lowered the temperature to a bitter -5°C. You hear a different
frequency from the siren before it passes you compared to after it passes you. What is the difference in the
frequencies you hear? 174 Hz
3.
You’re still traveling down the highway at 25 m/s when the ambulance returns, this time approaching you from
the front at the same 45 m/s. The temperature hasn't changed either. What is the difference in frequency you
hear this time as the ambulance approaches and then passes you? 609 Hz
4.
A train approaches a station at a speed of 34 m/s and sounds a 2000-Hz whistle. What is the change in
frequency heard as the train passes by? 400 Hz
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5.
An observer approaches a stationary 1000 Hz sound source at twice the speed of sound. What frequency does
the observer hear?
6.
If an X-15 jet, producing a frequency of 900 Hz, were moving away from you at 2.5 times the speed of sound,
what frequency would you hear? 257 Hz
7.
The wave below represents a sound wave from a siren heard by a stationary observer far away from the siren.
On the blank line below, draw what the sound wave would be like to the observer as he moved closer and
closer toward the siren at a high constant speed. (I’m looking for three things to be illustrated in your drawing).
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