Question 1

A violin string is 30 cm long and has a fundamental frequency of 440 Hz. If you want to play the note C (523 Hz), how far from the end of the string should you place your finger, assuming the tension and mass per unit length remain constant?

Accepted Answer

$$25\ \mathrm{cm}$$

Question 2

Which formula gives the speed of a longitudinal wave traveling through a volume (such as sound in air)?

Accepted Answer

$$v = \sqrt{\frac{B}{\rho}}$$

Question 3

A jet engine produces a sound intensity level of 130 dB at a certain distance $$r_0. At $$what distance will the intensity level be 110 dB, assuming isotropic emission and no absorption?

Accepted Answer

$$r = 100\ r_0$

Question 4

The beat frequency between two sound sources of frequencies $$f_1$$ and $$f_2 is $$given by:

Accepted Answer

$$\Delta f = |f_1$ - f_2$|$$

Question 5

A piano tuner hears 3 beats per second when striking a tuning fork ($$f = 523.3\ \mathrm{Hz}) $$and a piano key. After tightening the string, the beat frequency decreases to 2.0 beats per second. What was the original frequency of the piano string?

Accepted Answer

$$f = 526.3\ \mathrm{Hz}$$

Question 6

Which of the following best describes a node in a standing sound wave?

Accepted Answer

A point of zero displacement

Question 7

For a tube open at both ends, the wavelength of the $$nth $$harmonic is given by:

Accepted Answer

$$\lambda_n = \frac{2L}{n}$$

Question 8

The intensity level in decibels ($$\beta) is $$related to the intensity $$I by$$:

Accepted Answer

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

Question 9

A sensor on Mars records P-waves at $$t = 0.879 s $$and S-waves at $$t = 1.67 s$$, from a drilling operation 100 m away. If the density of Martian soil is $$1.37\ \mathrm{g/cm^3$}$$, what is the speed of the S-wave?

Accepted Answer

$$v_S = 59.9\ \mathrm{m/s}$$

Question 10

Which property of sound is most directly related to its intensity?

Accepted Answer

Loudness

Question 11

The Doppler effect causes a sound to be perceived as higher in pitch when:

Accepted Answer

The source moves toward the observer

Question 12

Which formula gives the speed of a transverse wave on a stretched string?

Accepted Answer

$$v = \sqrt{\frac{F_T}{\mu}}$$

Question 13

A clarinet is modeled as a tube closed at one end. Which harmonics are present in its sound spectrum?

Accepted Answer

Only odd harmonics

Question 14

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

Accepted Answer

$$20\ \mathrm{dB}$$

Question 15

Which of the following is a real-world application of standing waves?

Accepted Answer

Musical instruments

Question 16

The energy per unit area per unit time carried by a sound wave is called:

Accepted Answer

Intensity

Question 17

Which part of the ear is responsible for converting sound waves into electrical signals for the brain?

Accepted Answer

Cochlea

Question 18

A shock wave (sonic boom) occurs when:

Accepted Answer

An object moves faster than the speed of sound in the medium

Question 19

Ultrasound imaging relies on which physical principle?

Accepted Answer

Reflection of high-frequency sound waves

Lecture 24: Sound – Wave Properties, Intensity, Standing Waves, and Applications

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