Question 1

Which of the following best describes a transverse wave?

Accepted Answer

The displacement of particles is perpendicular to the direction of wave propagation.

Question 2

A string of length $$L$$ and mass $$m is $$under tension $$F. $$What is the correct formula for the speed of a wave on this string?

Accepted Answer

$$v = \sqrt{\frac{F}{\mu}}$$ where $$\mu = \frac{m}{L}$$

Question 3

If the frequency of a sound wave in air is doubled, what happens to its wavelength (assuming the speed of sound remains constant)?

Accepted Answer

The wavelength is halved.

Question 4

A sound wave travels in air at $$343\ \mathrm{m/s}. $$What is the frequency of a sound with a wavelength of $$1.31\ \mathrm{m}$$?

Accepted Answer

$$262\ \mathrm{Hz}$$

Question 5

A wave pulse on a string reflects from a fixed end. What happens to the pulse?

Accepted Answer

It is reflected and inverted.

Question 6

A guitar string has a mass per length of $$0.401 	imes 10$$^{-3}$$\ \mathrm{kg/m}$$ and is tightened to a tension of $$71.4\ \mathrm{N}. $$What is the speed of waves on the string?

Accepted Answer

$$119\ \mathrm{m/s}$$

Question 7

Which equation correctly gives the intensity $$I of a $$sound wave if the power passing through area $$A is$$ $$P$$?

Accepted Answer

$$I = \frac{P}{A}$$

Question 8

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

Accepted Answer

$$20\ \mathrm{dB}$$

Question 9

A bat emits a sound with power $$P$$ that spreads spherically. What is the intensity at a distance $$r$$ from the bat?

Accepted Answer

$$I = \frac{P}{4\pi r^2$}$$

Question 10

A person hears a sound with intensity $$I_1 at $$distance $$r_1$$ from a source. What is the intensity $$I_2 at $$distance $$r_2 ($$assuming spherical spreading and no absorption)?

Accepted Answer

$$I_2$$ = $$I_1$$ \left(\frac{$$r_1$$}{$$r_2$$}\$$right)^2$$

Question 11

Which of the following best describes the Doppler effect for a stationary observer and a moving source?

Accepted Answer

The observed frequency increases as the source moves toward the observer.

Question 12

A train approaches a tunnel at $$21.2\ \mathrm{m/s}$$, blowing a $$650\ \mathrm{Hz}$$ whistle. What frequency does an observer at rest near the tunnel entrance hear? (Speed of sound $$v = 343\ \mathrm{m/s})$$

Accepted Answer

$$689\ \mathrm{Hz}$$

Question 13

Which equation gives the sound intensity level $$\beta in $$decibels for intensity $$I$$ relative to reference intensity $$I_0$$?

Accepted Answer

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

Question 14

Two sound waves of frequencies $$f_1$$ and $$f_2$$ interfere to produce beats. What is the beat frequency?

Accepted Answer

$$|f_1$ - f_2$|$$

Question 15

A standing wave is formed on a string fixed at both ends. What is the wavelength of the fundamental mode if the string length is $$L$$?

Accepted Answer

$$\lambda = 2L$$

Question 16

A column of air closed at one end resonates at its fundamental frequency. If the length of the column is $$L$$, what is the wavelength of the fundamental mode?

Accepted Answer

$$\lambda = 4L$$

Question 17

If the tension in a string is doubled and its length is also doubled (mass remains the same), by what factor does the speed of waves on the string change?

Accepted Answer

$$1$$

Question 18

Which of the following is a real-world example of destructive interference?

Accepted Answer

Noise-cancelling headphones reducing ambient sound.

Question 19

A harmonic wave is described by $$y(x, t) = (0.12\ \mathrm{m}) \cos(\pi x/4 - 8\pi t). $$What is the period of this wave?

Accepted Answer

$$0.25\ \mathrm{s}$$

Chapter 14: Waves and Sound – Structured Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards