Define it!
A wave with a direction of propagation that is perpendicular to its direction of oscillation (like an ocean wave)
Transverse wave
#1a SG
The frequency of a wave can easily be drawn. Frequency indicates how many waves hit a certain point every second.
False
(Frequency can’t be drawn, but it does tell us
how many waves hit a point every second)
p. 342
Are sound waves transverse waves or longitudinal waves?
Longitudinal waves
#7 SG
Sound waves traveling through the air run into a wall. As they travel through the wall, do they go faster, slower, or at the same speed as through the air?
Faster
(Sound travels faster in solids than it does in gases or liquids.)
#9 SG
Two musical notes have the same pitch, but the first is louder than the second. Comparing the sound waves of each, what aspect(s) of the waves (wavelength, frequency, speed, & amplitude) would be the same?
Wavelength, frequency, & speed would be the same
(Amplitude is loudness, so the amplitude would be different.)
#15a SG
Do sound waves with low pitch have low frequency or high frequency?
Low frequency
(and sound waves with high pitch have high frequency)
p. 354
A wave with a direction of propagation that is parallel to its direction of oscillation
(like a sound wave)
Longitudinal wave
#1b SG
In a transverse wave, there are crests – the highest points – and troughs – the lowest points. The distance between the crests (or the troughs) is called the wavelength.
True
p. 342
Sound waves traveling through the air run into a wall. As they travel through the wall, is their amplitude smaller, larger, or the same?
Smaller
(As a wave strikes an obstacle, part of it is reflected and part of it is transmitted through. Since only a portion of it travels through the wall, the amplitude is smaller.)
#10 SG
Why do jets travel at speeds of Mach 1 or higher only in sparsely populated regions?
To avoid sonic booms close to people or buildings
(A jet traveling at Mach 1+up creates a shock wave of air, causing a very loud boom that can damage buildings and people’s ears.)
#13 SG
Two musical notes have the same pitch, but the first is louder than the second. Comparing the sound waves of each, what aspect(s) of the waves (wavelength, frequency, speed, & amplitude) would be different?
Amplitude would be different
(Amplitude is loudness, which was said to be different. The rest would be the same:
- Wavelength & frequency relate to pitch, said to be the same
- Speed depends only on temperature, which is not specified)
#15b SG
A physicist can hear an alarm sounding in an airtight chamber even though he is outside of the chamber. If he vacuum pumps the air out of the chamber, can he still hear the alarm?
No
(Without air, the sound waves from the alarm have nothing through which to travel. Thus, the alarm cannot make waves and there is no sound.)
#6a SG
Any speed that is faster than the speed of sound in the substance of interest
Supersonic speed
#1c SG
A longitudinal wave, such as a sound wave, moves like a slinky when you stretch it out in one direction.
True
(It oscillates between compressions – pushed together – and rarefactions – pulled apart. These are like the crests and troughs in transverse waves.)
p. 343
A sound wave with a wavelength of 500 meters is going 345 m/second. Is it infrasonic, sonic, or ultrasonic?
Infrasonic
What is the speed of a sound wave traveling through air with a temperature of 30 ºC?
Use speed of sound equation 14.2: v = (331.5 + 0.6 x T) m/sec
349.5 m/sec
[v = (331.5 + 0.6 x 30) m/sec
= (331.5 + 18) m/sec
= 349.5 m/sec]
#3 SG
A guitar player plucking on a string uses his finger to pinch it to the neck of the guitar, shortening its length. Will the pitch of the sound coming from the guitar increase, decrease, or stay the same?
Increase
(Since the string is made shorter, the wavelength is smaller and the frequency is higher. This means the pitch will increase.)
#14 SG
A physicist can hear an alarm going off in an airtight chamber even though he is outside of the chamber. But once he vacuum pumps the air out of the chamber, he can’t hear the alarm anymore - why?
Sound waves need air to travel through
(Without air, the sound waves from the alarm have nothing to travel through – so they can’t make waves; no waves = no sound.)
#6b SG
The sound produced as a result of an object traveling at or above Mach 1
Sonic boom
#1d SG
Engineers designing a car’s horn decide that its pitch is too low. To adjust the horn, they change the electronics to produce sound waves with shorter wavelengths.
True
(Wavelength and frequency are inversely proportional. For higher pitch, you need higher frequency, which means shorter wavelength.)
#2 SG
Standing near the highway, you raise your voice to about 80 decibels to be heard on a phone. The highway noise is about 100 decibels. How many times larger is the intensity of the traffic’s sound waves?
100 x larger
(Each bel unit increases the intensity of sound waves by a factor of 10. Calculate the bel units we are considering:
- Traffic = 100 decibels/1 x 0.1 bel/1 decibel = 10 bels
- Your Voice = 80 decibels/1 x 0.1 bel/1 decibel = 8 bels
Since traffic is 2 bels louder, the sound wave intensity is 2 factors of 10 higher than your voice, or 10 x 10 = 100 times larger.)
#18 SG
A jet is traveling at 464.1 m/sec in air that is 0 ºC. At what Mach number is the jet flying?
Use speed of sound equation 14.2:
v = (331.5 + 0.6 x T) m/sec
Then find out how many times faster than that the jet is traveling:
the speed of the jet (464.1 m/sec) divided by the speed of sound (v)
Remember! Mach IS the speed of sound.
Mach 1.4
(Speed of sound:
v = (331.5 + 0.6 x 0) m/sec
= 331.5 m/sec
How many times faster than sound the jet is traveling:
464.1 / 331.5 = 1.4]
#12 SG
The horn on your neighbor’s car is stuck, so it is constantly blaring. The neighbor gets into the car and drives away to get it fixed. Compare the pitch of the horn you hear before he starts to drive to the pitch you hear as he is driving away from you.
The pitch is lower as the car moves away
(As the car travels away from you, the horn’s sound waves get farther and farther apart. This makes the wavelength seem longer to your ears, which results in lower frequency. Lower frequency also means lower pitch.)
#16 SG
What is the following equation used to calculate for waves?
f=v/wavelength
(This is equation 14.1. Remember, aspects of waves are: wavelength, frequency, speed, and amplitude.)
Frequency
(It can also find wavelength or speed of a wave if we know the frequency and the other variable.)
p. 342
An indication of how high or low a sound is, which is primarily determined by the frequency of the sound wave
Pitch
#1e SG
Going at 349.5 m/sec, if the sound wave’s frequency has a wavelength of 0.5 meters, its frequency is 699 Hz. [Use equation 14.1; frequency (F) = speed (v)/wavelength (gamma symbol)]
True
F =
349.5 m/s/0.5m
F =
699/sec
F = 699 Hz
#4 SG
An amplifier can magnify the intensity of sound waves by a factor of 1,000. If a 30-decibel sound is fed into the amplifier, how many decibels will come out?
60 decibels
(Each bel unit increases the intensity of sound waves by a factor of 10. Calculate the bel units we are considering:
- Initial Sound = 30 decibels/1 x 0.1 bel/1 decibel = 3 bels
- Amplifier = magnifies by 1,000 = 10 x 10 x 10 = 3 bels
The initial sound of 3 bels + the amplifier’s 3 bels = 6 bels or 60 decibels.)
#19 SG
A jet is traveling at Mach 2.5 through air at 1 ºC. What is the jet’s speed in m/sec?
Use speed of sound equation 14.2:
v = (331.5 + 0.6 x T) m/sec
Then multiply by the Mach speed of the jet:
sound speed (v) x jet speed (Mach 2.5)
Remember! Mach IS the speed of sound.
830.25 m/sec
[Speed of sound: v = (331.5 + 0.6 x 1) m/sec
= (331.5 + 0.6) m/sec
= 332.1 m/sec
Multiply by the Mach speed of the jet:
= 2.5 x (332.1 m/sec)
= 830.25 m/sec]
#11 SG
You ride your bike toward a parked police car with a blaring siren. Is the pitch of the siren sound lower, higher, or the same as it will be when you stop your bike? (Assume the actual pitch of the siren stays constant.)
Higher
(Riding towards the police car, you will encounter the compressions of the sound waves faster than when you stand still. So the wavelength will seem shorter to you, which will cause you to hear higher frequencies. Higher frequencies also mean higher pitch.)
#17 SG
You see a flash of lightning and 2.3 seconds later you hear the thunder. The outside temp is 13˚C. How far are you from where the lightning struck?
Use speed of sound equation 14.2:
v = (331.5 + 0.6 x T) m/sec
Then distance equation 14.3:
D = (speed) x (time traveled)
780.39 m
[Speed of sound:
v = (331.5 + 0.6 x 13) m/sec
= (331.5 + 7.8) m/sec
= 339.3 m/sec
Distance, assuming you saw it instantly:
D = (339.3 m/sec) x (2.3 sec)
= 780.39 m]
#8 SG