17 Sound
17 Chapter Review
Key Terms
- beat frequency
- frequency of beats produced by sound waves that differ in frequency
- beats
- constructive and destructive interference of two or more frequencies of sound
- bow wake
- v-shaped disturbance created when the wave source moves faster than the wave propagation speed
- Doppler effect
- alteration in the observed frequency of a sound due to motion of either the source or the observer
- Doppler shift
- actual change in frequency due to relative motion of source and observer
- fundamental
- the lowest-frequency resonance
- harmonics
- the term used to refer collectively to the fundamental and its overtones
- hearing
- perception of sound
- loudness
- perception of sound intensity
- notes
- basic unit of music with specific names, combined to generate tunes
- overtones
- all resonant frequencies higher than the fundamental
- phon
- numerical unit of loudness
- pitch
- perception of the frequency of a sound
- shock wave
- wave front that is produced when a sound source moves faster than the speed of sound
- sonic boom
- loud noise that occurs as a shock wave as it sweeps along the ground
- sound
- traveling pressure wave that may be periodic; the wave can be modeled as a pressure wave or as an oscillation of molecules
- sound intensity level
- unitless quantity telling you the level of the sound relative to a fixed standard
- sound pressure level
- ratio of the pressure amplitude to a reference pressure
- timbre
- number and relative intensity of multiple sound frequencies
- transducer
- device that converts energy of a signal into measurable energy form, for example, a microphone converts sound waves into an electrical signal
Key Equations
| Pressure of a sound wave | [latex]\Delta P=\Delta {P}_{\text{max}}\text{sin}(kx\mp \omega t+\varphi )[/latex] |
| Displacement of the oscillating molecules of a
sound wave |
[latex]s(x,t)={s}_{\text{max}}\text{cos}(kx\mp \omega t+\varphi )[/latex] |
| Velocity of a wave | [latex]v=f\lambda[/latex] |
| Speed of sound in a fluid | [latex]v=\sqrt{\frac{\beta }{\rho }}[/latex] |
| Speed of sound in a solid | [latex]v=\sqrt{\frac{Y}{\rho }}[/latex] |
| Speed of sound in an ideal gas | [latex]v=\sqrt{\frac{\gamma RT}{M}}[/latex] |
| Speed of sound in air as a function of temperature | [latex]v=331\frac{\text{m}}{\text{s}}\sqrt{\frac{{T}_{\text{K}}}{273\,\text{K}}}=331\frac{\text{m}}{\text{s}}\sqrt{1+\frac{{T}_{\text{C}}}{273^\circ\text{C}}}[/latex] |
| Decrease in intensity as a spherical wave expands | [latex]{I}_{2}={I}_{1}{(\frac{{r}_{1}}{{r}_{2}})}^{2}[/latex] |
| Intensity averaged over a period | [latex]I=\frac{〈P〉}{A}[/latex] |
| Intensity of sound | [latex]I=\frac{{(\Delta {p}_{\text{max}})}^{2}}{2\rho v}[/latex] |
| Sound intensity level | [latex]\beta (dB)=10\,{\text{log}}_{10}(\frac{I}{{I}_{0}})[/latex] |
| Resonant wavelengths of a tube closed at one end | [latex]{\lambda }_{n}=\frac{4}{n}L,n=1,3,5\text{,…}[/latex] |
| Resonant frequencies of a tube closed