Waves and Sound Study Guide
Name: KEY
1. How do certain factors influence the motion of a pendulum? From the lab, what influence the period of the
pendulum the most? Why? the length of the pendulum influenced the most because the other factors
depend on gravity and gravity remains constant
2. What are the three types of waves, and how are they different in the way they move?
a. transverse-particles travel perpendicular to the direction of wave motion
b. longitudinal-particles travel parallel to the direction of wave motion
c. surface-particles travel both parallel and perpendicular to the direction of wave motion
3. Label the wavelength, amplitude, crest, trough, and identify many wavelengths are present in the given wave.
Draw in the equilibrium line.
amplitude
crest
wavelength
wavelength
equilibrium line
trough
wavelength
4. What are the two types of interference, and how are they different? Draw a picture.
constructive – when two in-phase waves meet and a wave with a larger amplitude results; crest meets crest or
trough meets trough
destructive - when two out-of-phase waves meet and a wave with a smaller amplitude results; crest meets
trough
See notes for picture.
5. What do in phase and out of phase mean?
in-phase – waves that have the same frequency and pass through corresponding positions at the same time;
crest meets crest; trough meets trough
out-of-phase – waves that pass through corresponding positions at different times; crest meets trough
6. How do beats form? Draw a picture.
Beats form when two notes of slightly different (or similar) frequencies are sounded at the same time.
See notes/book for picture.
7. How do standing waves form? Draw a picture and identify the incident wave and the reflected wave
Standing waves are produce when two traveling waves of the same frequency move in opposite directions.
See notes for picture
8. What happens to standing waves when the tension and frequency are changed? (Hint: think about the lab)
OMIT.
9. Label the nodes and antinodes in the standing wave below.
antinodes
What harmonic is this wave? 2nd harmonic
nodes
If this wave was found at 18 Hz, where would you find the 5th harmonic? f1 = (18 Hz)/2 = 9 Hz so f5 = (9 Hz)(5) =
45 Hz
10. What is a sound wave, and how does it move?
Sound waves are longitudinal waves caused by vibrations.
11. What is loudness, and how do we determine and measure it?
Loudness is a measure of the energy of a sound wave. The amplitude of the sound wave determines the
loudness of the sound. The unit for loudness is the decibel.
12. What is the speed of sound, and how does it vary in different mediums?
The speed of sound in air is approximately 340 m/s. Sound travels fastest in solids and warmer temperatures.
13. What is the Doppler shift, and how does relative motion influence pitch? You may use a picture to help explain.
The Doppler shift is the apparent change in frequency due to the motion of a sound or the observer. When the
sound is approaching the pitch is higher and when the sound is moving away the pitch is lower.
Wave Practice Problems
v  f
f 
1
T
16. A guitar string makes 80 vibrations in one second. What is the period? What is the frequency?
f = 80 Hz and T = 0.0125 s
17. A drum vibrates 180 times in 2 seconds. If the speed of sound is 340 m/s, what are the period, frequency and
wavelength of the waves produced by the drum?
f = 90 Hz, T = 0.011 s, and λ = 3.8 m
18. The speed of light is 3 X 108 m/s. If blue light has a frequency of 6 X 106 Hz, what is the period and wavelength
of blue light?
T = 1.7 x 10-7 s and λ = 50 m
19. A butterfly flaps its wings 100 times in 10 seconds. What is the period and frequency? If the speed of sound is
340 m/s, what is the wavelength of the sound waves produced?
T = 0.1 s, f = 10 Hz, and λ = 34 m
20. A 10 m long rope is used to create standing waves. If the rope makes 240 vibrations in one minute, what is the
period and frequency of the waves? If the waves are traveling 12 m/s, what is the wavelength of the waves and
how long does it take a single wave to travel from one end of the rope to another?
T = 0.25 s, f = 4 Hz, λ = 3 m, and t = 0.83 s
For all problems, assume the speed of sound in air is 343 m/s and the speed of all electromagnetic waves is 3 x 108
m/s unless otherwise noted
21. A radio wave, a form of electromagnetic wave, has a frequency of 99.5 MHz (99.5 x 106 Hz). What is its
wavelength?
λ = 3.02 m
22. Sound with a frequency of 261.6 Hz travels through water at a speed of 1435 m/s. Find its wavelength in water.
λ = 5.485 m
23. Find the frequency of a sound wave moving in air at room temperature with a wavelength of 0.667 m.
f = 514 Hz
24. Water waves in a shallow dish are 10 cm long. The water oscillates up and down at a rate of 4.8 oscillations per
second.
1. What is the speed that the waves move through the water? v = 0.48 m/s
2. What is their period? f = 4.8 Hz so T = 0.21 s
25. Water waves in a lake travel 6.2m in 2.3 s. Their period of oscillation is 1.8s.
1. What is the speed that the waves move through the water? v = 2.7 m/s
2. What is their wavelength? λ = 4.9 m
26. The human ear can detect sounds with frequencies between 20 Hz and 16 kHz. Find the largest and smallest
wavelengths the ear can detect in room temperature air.
λ = 17 m to 0.021 m
27. What is the frequency of a sound in room temperature air if it has a wavelength of 38 cm? of 7.6 cm?
f = 903 Hz and f = 4513 Hz
28. A sound wave produced by a clock chime 515 m away is heard 1.60 s later.
1. What is the speed of sound in the surrounding air? v = 322 m/s
2. The sound wave has a frequency of 436 Hz. What is its period? T = 0.00229 s
3. What is its wavelength? λ= 0.739 m
29. A hiker shouts toward a vertical cliff 685 m away. The echo is heard 4.00 s later.
1. What is the speed of sound in the surrounding air? v = 343 m/s
2. The wavelength of the sound is 0.750 m. What is its frequency? f = 457 Hz
3. What is the period of the wave? T = 0.00219 s
30. A sonar unit on a submarine sends out a pulse of sound into seawater. The pulse returns 2.78 s later. What is
the distance between the object and the submarine? The speed of sound in seawater is 1522 m/s.
d = 2116 m
31. If you want to increase the wavelength of waves in a rope, should you shake it at a higher or lower frequency?
longer wavelength = lower frequency
32. If the pitch of sound increases, what happens to its:
1. Frequency? increases
2. Wavelength? decreases
3. Velocity? remains the same
4. Amplitude? remains the same
33. As a wave moves from a medium with a high wave velocity to one with a smaller wave velocity, which of the
following CANNOT/WON’T change: frequency, amplitude, wavelength, velocity, direction?
the frequency is the only one that will NOT change