Ch 16: Sound and Hearing

Question 1

sound

Answer 1

longitudinal wave in a medium

Question 2

audible range

Answer 2

20 to 20,000 Hz

Question 3

ultrasonic

Answer 3

having a frequency above range of human hearing

Question 4

infrasonic

Answer 4

having a frequency below range of human hearing

Question 5

Sound waves usually travel ______.

Answer 5

out in all directions from the source of sound

Question 6

displacement amplitude

Answer 6

same as amplitude

Question 7

p(x,t) is _____.

Answer 7

the instantaneous pressure fluctuation in a sound wave at any point x at time t; the amount by which the pressure differs from normal atmospheric pressure; AKA gauge pressure

Question 8

pressure amplitude

Answer 8

maximum pressure fluctuation; p_max= BkA

Question 9

Waves of shorter wavelength have greater _____ because _____.

Answer 9

pressure variations for a given amplitude; the maxima and minima are squeezed closer together

Question 10

bulk modulus

Answer 10

B= -p(x,t)/(dV/V)

Question 11

A medium with a large value of bulk modulus requires a relatively large _____ because _____.

Answer 11

pressure amplitude for a given displacement amplitude; large B means a less compressible medium; greater pressure change is required for a given volume change

Question 12

What determines loudness?

Answer 12

the pressure amplitude: the greater the pressure amplitude, the greater the loudness

Question 13

What determines pitch?

Answer 13

the frequency of a sound wave; the higher the frequency, the higher the pitch

Question 14

harmonic content

Answer 14

the amount of harmonics

Question 15

Fourier analysis

Answer 15

the mathematical process of translating a pressure-time graph into a graph of harmonic content

Question 16

Why do 2 different instruments producing the same note (same fundamental frequency, same pitch) sound different Why do the letters “a” and “e” sound different?

Answer 16

They have different harmonic content.

Question 17

noise

Answer 17

combination of all frequencies

Question 18

What are the different ways to describe a sound wave?

Answer 18

displacement vs position graph, drawing showing displacements of individual particles, and pressure fluctuation vs. position graph

Question 19

speed of a longitudinal wave in a fluid

Answer 19

v = √B/ρ, where B is the Bulk modulus

Question 20

speed of a longitudinal wave in a solid

Answer 20

v = √Y/ρ, where Y is Young’s Modulus

Question 21

speed of sound in an ideal gas

Answer 21

v = √γRT/M, where γ is the ratio of heat capacities and M is the molar mass of the gas

Question 22

intensity of a longitudinal sound wave

Answer 22

I = 1/2 sqrt(ρB)ω^2 A^2

Question 23

Sinusoidal sound waves of the same intensity but different frequency have different _____ but the same _____.

Answer 23

displacement amplitudes A; pressure amplitude p_max

Question 24

If a sound wave goes predominantly in one direction, the inverse square law for intensity _____.

Answer 24

does not apply and the intensity decreases with distance more slowly than 1/r^2

Question 25

The inverse square law for intensity does not apply indoors because _____.

Answer 25

sound energy can reach a listener by reflection

Question 26

sound intensity level

Answer 26

β = (10dB) log I/I_0, where I_0 is a reference intensity, chosen to be 10^-12 W/m^2

Question 27

decibel

Answer 27

unit of sound intensity level