Chapter 11 and 12 Test Review:
1. A sound wave is a longitudinal, mechanical wave which means it
a) Amplitude is parallel to wave motion
b) it requires a medium to travel through.
2. The threshold of hearing in Decibels is _0___ , and __10-12__ in W/m2, and 20____ in Hz
3. Compared to the threshold of hearing, a sound level of 50 decibels is how many times more intense.
Show work:
50 = 10 Log I/10-12 5 = log I/10-12 105 = I/10-12 = 10-7 so 105 or 100,000 times more intense.
4. The Doppler Effect is the phenomena of hearing a different pitch as a source approaches or recedes.
Explain why the pitch changes. As sound moves, the waves received are either compressed
(approaching) or elongated (moving away).
5. Will the pitch be higher or lower as you approach a sound source? __higher___
6. How are period and frequency related? ______They are reciprocals____________
7. Given this relationship if you triple the frequency of a vibrating object, its period will _____decrease by
1/3rd__.
8. Draw a transverse wave and label the following parts: crest, trough, wavelength, amplitude. Then define
the frequency and velocity of the wave
Frequency: # of cycles per second.
Velocity: Speed of the wave. V = fλ
9. Define all the parts of a compression (longitudinal) wave: rarefaction, compression, amplitude,
period, frequency, wave speed.
Period – Time for one cycle, Frequency - # of cycles per second, Wave Speed – how fast the wave travels
in m/s.
10. Which part of the wave represents intensity or loudness? Amplitude
11. What do we call the TIME needed for wave or oscillation to complete on cycle?
Period
12. Explain how sound energy is propagated. Vibrating molecules strike nearby molecules and the sound
propagates though the media.
13. What is the difference between pitch and frequency? Pitch is qualitative and depends on the listener.
Frequency is quantitative and is based on source.
14. Points of constructive interference are called ___anti-nodes__ and parts of destructive interference are
called ____nodes____ in a standing wave?
15. The beat frequency is how often we hear the beat occurring between two frequencies. Calculate the beat
frequency between a 300 Hz and a 310 Hz source.
10 beats/s
16. What is the relative intensity of a sound which has an intensity of 10-9 W/cm2?
dB = 10 log 10-9/10-12 = 30 dB
17. What is the intensity of a sound which has a relative intensity 110 dB?
110 dB = 10 log I/10-12
11 = Log I/10-12
1011 * 10-12 = I
I = 0.1 W/m2
18. What is the speed of sound at room temperature (25°C)? _346 m/s_____________
19. How can we determine the wavelength of sound at room temperature if the frequency is 400 Hz?
V = fλ
346 m/s = (400 hz)(λ)
λ = 0.865 m
20. Calculate the frequency of a 15 m wave traveling at 1000 m/s.
V = fλ
f = 66.6 hz
21. While you are sitting at a railroad crossing waiting for an approaching train, the engineer sounds the
whistle (f = 500 Hz).
a. If the train is approaching at 20 m/s and the air temperature is 20 C, what frequency will you
hear?
530 Hz
b. After the train passes you the whistle sounds again, now what frequency will you hear?
472.5 Hz
22. You are driving through the neighborhood and pass a car whose alarm is going off (f = 700 Hz).
a. If you are obeying the speed limit of 25 mph (11.3 m/s), what frequency will you hear as you
approach the car?
723 Hz
b. What frequency will you hear after you pass the car?
676.9 Hz
antinode
23. On the diagram to the right:
A. label the nodes and antinodes.
B. What is its wavelength if the distance between
nodes is 2 m? ________
0m
4 meters
2m
4m
6m
node
C. If the person is shaking her hand up-and-down 12 times per second, what is the wave velocity? (Show
Work)
48 m/s
24.. In each set of waves below, the two waves at the left represent two waves traveling at the same time. You
are to combine the two waves and show the results at the right.
a)
b)
24. What is the period of a pendulum which is 1.5 meters long at sea level?
2.46 seconds
25. A closed pipe has a length of 2.5 meters. Calculate the fundamental frequency of the pipe and its first
two harmonics at room temperature (25 °C)?
λ = 4L
λ = 10 m
V = 346 m/s
f = V/λ = 34.6 hz
3f = 103.8 hz
5f = 173 hz
26. A spring stretches 0.150 m when a 0.300 kg mass is attached to it. The spring is then stretched an
additional 0.1 m from its equilibrium point and released. Find
a. the spring constant K
K = F/X
K = (0.3 kg)(9.8 m/s2) /0.15 m = 19.6 N/m
b. The amplitude of the oscillation
A = 0.1 meters
c. The maximum velocity
𝑁
19.6
𝐾
𝑚 = 0.808 𝑚/𝑠
𝑉 = 𝐴√ = (0.1 𝑚)√
𝑚
0.3 𝑘𝑔