Q: If a source of sound moves toward a stationary observer, which equation gives the observed frequency?

$$f' = \frac{f}{1 - \frac{v_{\text{source}}}{v_{\text{snd}}}}$$

Question 1

Which of the following materials allows sound to travel the fastest, according to the provided table?

Accepted Answer

Aluminum

Question 2

A loud rock concert has a sound intensity of $$1\ 	ext{W/m}^2. $$What is the sound level in decibels (dB) for this intensity, given that $$I_0 = 1.0$$ 	imes $$10^{-12}$$\ 	ext{W/m}^2$$?

Accepted Answer

$$\beta = 120\ 	ext{dB}$$

Question 3

If a sound wave of frequency 220 Hz travels through air at 343 m/s, what is its wavelength?

Accepted Answer

$$\lambda = 1.56\ 	ext{m}$$

Question 4

A cylindrical pipe is closed at one end and has a fundamental frequency of 100 Hz. Which of the following frequencies will NOT resonate in this pipe?

Accepted Answer

400 Hz

Question 5

What happens to the fundamental frequency of a cylindrical pipe if the closed end is opened?

Accepted Answer

It rises by an octave.

Question 6

A train blowing its horn is approaching you with constant speed. The apparent pitch you hear is:

Accepted Answer

Higher than the real one.

Question 7

The intensity of sound diminishes with distance in open areas according to which relationship?

Accepted Answer

$$I \propto \frac{1}{r^2$}$$

Question 8

Which equation correctly describes the sound level in decibels?

Accepted Answer

$$\beta = 10 \log \frac{I}{I_0$}$$

Question 9

For a string fixed at both ends, the distance between two adjacent nodes is:

Accepted Answer

Half of the wavelength of vibration

Question 10

A guitar string is shortened by pressing it against a fret. What happens to the fundamental frequency?

Accepted Answer

It increases

Question 11

If the frequency of a sound wave is doubled, but the speed remains constant, what happens to the wavelength?

Accepted Answer

It is halved

Question 12

Which of the following best describes the motion of air particles when sound travels from left to right in a classroom?

Accepted Answer

In the left-right direction

Question 13

A whisper has an intensity of $$1 	imes 10$$^{-10}$$\ 	ext{W/m}^2. $$What is its sound level in decibels?

Accepted Answer

$$\beta = 50\ 	ext{dB}$$

Question 14

Which frequency will resonate in a tube closed at one end with a fundamental frequency $$f_1$$?

Accepted Answer

$$3f_1$$

Question 15

If a source of sound moves toward a stationary observer, which equation gives the observed frequency?

Accepted Answer

$$f' = \frac{f}{1 - \frac{v_{	ext{source}}}{v_{	ext{snd}}}}$$

Question 16

You perform two Doppler shift experiments with a car siren moving at 60 mph, once at 0°C and once at 40°C. Which set will show a greater Doppler shift?

Accepted Answer

Set at 40°C

Question 17

Which of the following is true about the audible range of human hearing?

Accepted Answer

It is about 20 Hz to 20,000 Hz

Question 18

A wind instrument with both ends open produces a fundamental frequency $$f_1. $$What is the frequency of its second harmonic?

Accepted Answer

$$2f_1$$

Question 19

Which property of sound is most closely related to the frequency of the wave?

Accepted Answer

Pitch

Question 20

A fire truck is moving toward an observer. What happens to the wavelength and frequency of the sound observed?

Accepted Answer

Wavelength decreases, frequency increases

Chapter 12: Sound – Properties, Intensity, Sources, and the Doppler Effect

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