Q: A supersonic jet travels at Mach 2. If the speed of sound is 340 m/s, what is the Mach angle $$\theta of $$the shock wave?

$$\theta = \arcsin\left(\frac{1}{2}\right) = 30^\circ$$

Question 1

Which of the following best describes the difference between a longitudinal and a transverse wave, as applied to sound in air?

Accepted Answer

In a longitudinal wave, particle displacements are parallel to the direction of wave propagation, while in a transverse wave, they are perpendicular.

Question 2

The speed of sound in an ideal gas is given by which of the following equations?

Accepted Answer

$$v = \sqrt{\frac{\gamma RT}{M}}$$

Question 3

A sound wave in water has a pressure amplitude $$p_{max}$$ and propagates with speed $$v. $$What is the intensity $$I of $$this wave?

Accepted Answer

$$I = \frac{p_{max}^2}{2 \rho v}$$

Question 4

A person hears a beat frequency of 5 Hz when two tuning forks are sounded together. If one fork vibrates at 256 Hz, what are the possible frequencies of the other fork?

Accepted Answer

251 Hz or 261 Hz

Question 5

Which of the following statements about the Doppler effect is correct?

Accepted Answer

When a sound source moves toward a stationary observer, the observed frequency increases.

Question 6

A closed pipe (one end closed, one end open) of length $$L$$ supports a standing wave at its third harmonic. What is the wavelength $$\lambda of $$this harmonic?

Accepted Answer

$$\lambda = \frac{4L}{3}$$

Question 7

The sound intensity level $$\beta in $$decibels is defined as:

Accepted Answer

$$\beta = (10\ \mathrm{dB}) \log_{10}\left(\frac{I}{I_0$}\right)$$

Question 8

A sound wave travels from air into water. Which of the following statements is true?

Accepted Answer

The speed of sound increases because water is denser and has a higher bulk modulus than air.

Question 9

Two loudspeakers emit sound waves of the same frequency and are in phase. At a certain point, the path difference from the two speakers to the point is $$\frac{3}{2}\lambda. $$What type of interference occurs at this point?

Accepted Answer

Destructive interference

Question 10

A supersonic jet travels at Mach 2. If the speed of sound is 340 m/s, what is the Mach angle $$	heta of $$the shock wave?

Accepted Answer

$$	heta = \arcsin\left(\frac{1}{2}ight) = 30^\circ$$

Question 11

A flute (open at both ends) and a clarinet (closed at one end) are both 0.68 m long. Which instrument can produce a lower fundamental frequency, and why?

Accepted Answer

The clarinet, because its fundamental wavelength is four times its length.

Question 12

A sound wave with frequency $$f$$ and wavelength $$\lambda$$ travels in air. If the temperature increases, what happens to the speed $$v$$ and wavelength $$\lambda of $$the sound, assuming $$f is $$constant?

Accepted Answer

Both $$v$$ and $$\lambda$$ increase.

Question 13

A person is tuning a violin string and hears 4 beats per second when played with a 440 Hz tuning fork. After tightening the string, the beat frequency increases. What should the person do to tune the string correctly?

Accepted Answer

Loosen the string until the beats disappear.

Question 14

Which of the following best explains why you can hear someone talking through an open doorway even if you cannot see them?

Accepted Answer

Sound waves diffract through the opening and spread out.

Question 15

A sound wave in air has a frequency of 1000 Hz and a wavelength of 0.34 m. What is the speed of sound in air under these conditions?

Accepted Answer

$$v = f \lambda = 1000 	imes 0.34 = 340\ \mathrm{m/s}$$

Question 16

Which of the following is a real-world application of the Doppler effect?

Accepted Answer

Measuring blood flow using Doppler ultrasound.

Question 17

If the intensity of a sound increases by a factor of 100, by how many decibels does the sound intensity level increase?

Accepted Answer

20 dB

Question 18

Which of the following best describes the effect of sound attenuation in a material?

Accepted Answer

Sound intensity decreases with distance due to absorption and scattering.

Question 19

A standing wave is set up in a pipe closed at one end and open at the other. If the pipe is 0.5 m long, what is the fundamental frequency if the speed of sound is 340 m/s?

Accepted Answer

$$f_1$$ = \frac{v}{4L} = \frac{340}{4 	imes 0.5} = 170\ \mathrm{Hz}$$

Chapter 16: Sound and Hearing – Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards