Summary LAB NOTES: WEEK 10 OF PHYSICS3LC AT UCI

Wk10--The Attenuation of Sound Abbreviations:
Sunday, December 6, 2020 9:48 PM b/w = between
w/ = with
INC = increase
DEC = decrease

• Sound waves propagate in air as pressure. -> The amplitude of a sound wave is


measured by the amount of INC or DEC in pre above or below the ambient pressure.


• Transmitted wave: the new sound wave transmitted when a sound wave hits a solid


and the solid pushes on the air behind it.


○ Pt: amplitude of the transmitted wave. Depends on the mass per unit area of the


wall σ and the frequency of the wave v:


○
𝑝𝑡/𝑝𝑖 = sqrt[1 / (1+(𝜋𝑣𝜎/𝜌𝑣)2)] Eqn 10.1, approximation



○ where pi is the amplitude of the incident wave and ρ is the density of


air(velocity on bottom). Ratio pt/pi is the transmission coefficient. -> What


fraction of the wave is being transmitted?


○ Eqn 10.1 is only an approximation due to diffraction and reflections off the


attenuator/other surfaces that could lead to deviations.


• Velocity of the sound waves u: u = vl, where l is wavelength. Constant at 344m/s in


air at 20C.


• You will place various attenuators between the two speakers and measure how much


they affect the amplitude of the sound waves received by the second speaker.