PHYSCI 101 Chapter 6 HW Answers
Multiple Choice:
1. b
"A wave with a particle oscillation parallel to the direction of propagation is a longitudinal wave."
2. a
Transverse waves have vibrations that are perpendicular to the direction of propagation.
5. d
All electromagnetic waves travel at the same speed in a vacuum, are transverse waves, and can travel
without a medium.
10. a Approaching a stationary observer results in an increase in frequency
12. a A star moving toward us would have an atomic spectrum that is blue shifted.
Short Answer:
6. The numbers can read from the graph.
a. Amplitude = 2 cm
b. Frequency = 1.75 Hz
(1.75 cycles in the one second)
8. Visible Spectrum
a. Longer wavelength: Red
b. Higher Frequency: Blue
9. Radio waves are not sound waves. Radio waves are part of the electromagnetic spectrum; they are "light"
waves.
11. A rarefaction is the spreading out of molecules as sound wave vibrations move through a material.
18. Light travels faster than sound.
 Lightening is a light wave and all light waves travel at about 3 x 108 m/s in air.
 Thunder is a sound wave and sound waves travel at an average of 343 m/s in air.
Applying Your Knowledge:
2. A person standing on the Moon would not here the hammer drop because there is no atmosphere. Sound
requires a medium through which the vibration may travel.
Now if the astronaut's head were in direct contact with the ground, the vibration might propagate through the
helmet causing the air inside the helmet to vibrate, resulting in sound. (not very likely)
4. A “jet” fish would have to swim at the speed of sound in water which is 1484 m/s (3320 mph!)
T. Ciardi
Chapter 6 HW Answers
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Exercises:
4. Sound wave, so we know the speed.
v = 344 m/s
f = 3000 Hz
The distance between crests is the wavelength. Speed wavelength and frequency are related to each
other in an equation.
v = f
Solve for the wavelength, and enter the numbers
 = v = 344 m/s = 0.115 m
f
3,000 Hz
6. An x-ray travels at the speed of light.
v = 3 x 108 m/s
f = 1018 Hz
v = f
 = v = 3 x 108 m/s = 3 x 10–10 m = 0.3 nm
f
1018 Hz
10. Telephone signals travel at the speed of light.
v = 3 x 108 m/s
a. Time to travel across the country
t=?
d = 3,000 miles
First we need to convert miles to standard units.
3,000 miles x 1609 m = 4.827 x 106 m
1 mile
The equation we need is the equation for speed. Solve for time and enter the numbers.
s=d
t
t = d = 4.827 x 106 m = 0.016 seconds
s
3 x 108 m/s
T. Ciardi
Chapter 6 HW Answers
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b. Time to travel to international space station
t=?
d = 350 km = 350,000 m
t = d = 350,000 m = 0.0012 seconds
s
3 x 108 m/s
Additional:
1.
a. Short to Long 
X-rays
Ultraviolet
Blue light
Green light
Yellow Light
Red light
Infrared
Microwaves
Radio
b. Low to High f
Radio
Microwaves
Infrared
Red light
Yellow light
Green light
Blue light
Ultraviolet
X-rays
2. Sound wave
v = 344 m/s
f = 261.6 Hz
= ?
v = f
 = v = 344 m/s = 1.3 m
f
261.6 Hz
Extra Credit Challenge: (3 points)
16.
v = 344 m/s (thunder is sound)
t = 9.0 s
s(cloud) = 15 km/h
First, we need to determine the distance between the storm and the picnickers.
d = st = (344 m/s)(9 s) = 3,096 meters = 3 km
Now we can determine how long it will take for the storm to move that distance.
t = d = 3 km = 0.2 hour = 12 minutes
s
15 km/h
T. Ciardi
Chapter 6 HW Answers
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