Section 1
Properties and Detection of Sound
Find the wavelength in air at $20^{\circ} \mathrm{C}$ of an $18-\mathrm{Hz}$ sound wave, which is one of the lowest frequencies that is detectable by the human ear.
What is the wavelength of an $18-\mathrm{Hz}$ sound wave in seawater at $25^{\circ} \mathrm{C} ?$
Find the frequency of a sound wave moving through iron at $25^{\circ} \mathrm{C}$ with a wavelength of $1.25 \mathrm{m}$
If you shout across a canyon and hear the echo 0.80 s later, how wide is the canyon?
A $2280-\mathrm{Hz}$ sound wave has a wavelength of $0.655 \mathrm{m}$ in an unknown medium. Identify the medium.
Repeat Example Problem 1, but with the car moving away from you. What frequency would you hear?
You are in an auto traveling at $25.0 \mathrm{m} / \mathrm{s}$ toward a pole-mounted warning siren. If the siren's frequency is $365 \mathrm{Hz}$, what frequency do you hear? Use $343 \mathrm{m} / \mathrm{s}$ as the speed of sound.
You are in an auto traveling at 55 mph $(24.6 \mathrm{m} / \mathrm{s}) .$ A second auto is moving toward you at the same speed. Its horn is sounding at 475 Hz. What frequency do you hear? Use $343 \mathrm{m} / \mathrm{s}$ as the speed of sound.
A submarine is moving toward another submarine at $9.20 \mathrm{m} / \mathrm{s}$ It emits a 3.50 -MHz ultrasound. What frequency would the second sub, at rest, detect? The speed of sound in water is $1482 \mathrm{m} / \mathrm{s}$
A sound source plays middle $\mathrm{C}(262 \mathrm{Hz})$. How fast would the source have to go to raise the pitch to $\mathrm{C}$ sharp $(271 \mathrm{Hz}) ?$ Use $343 \mathrm{m} / \mathrm{s}$ as the speed of sound.
The eardrum moves back and forth in response to the pressure variations of a sound wave. Sketch a graph of the displacement of the eardrum versus time for two cycles of a $1.0-\mathrm{kHz}$ tone and for two cycles of a 2.0 -kHz tone.
List two sound characteristics that are affected by the medium through which the sound passes and two characteristics that are not affected.
What physical characteristic of a sound wave should be changed to change the pitch of the sound? To change the loudness?
How much greater is the sound pressure level of a typical rock band's music (1 $10 \mathrm{dB}$ ) than a normal conversation $(50 \mathrm{dB}) ?$
In the nineteenth century, people put their ears to a railroad track to get an early warning of an approaching train. Why did this work?
A bat emits short pulses of high-frequency sound and detects the echoes.a. In what way would the echoes from large and small insects compare if they were the same distance from the bat?b. In what way would the echo from an insect flying toward the bat differ from that of an insect flying away from the bat?
Can a trooper using a radar detector at the side of the road determine the speed of a car at the instant the car passes the trooper? Explain.