A sound wave traveling in 20ºC air has a pressure amplitude of 0.5 Pa. What is the intensity of the wave?

1 Answer
Feb 21, 2015

#I=3.03×10^(-4)W/m^2.#

Intensity is defined as power over an area. It's given by

#I=P/A#

where
#I -># intensity; #W/m^2#
#P-># power; #W#
#A -># area; #m^2#

The intensity of a sound wave is given by the following eq'n:

#I=(Deltap)^2/(2rhov_w)#

where
#I -># intensity; #W/m^2#
#Deltap -># pressure variation/pressure amplitude #Pa or N/m^2#
#rho -># density of material; #(kg)/m^3#
#v_w -># speed of sound in medium; #m/s#

Given this equation, along with constants, you can substitute your values and solve.

The constant for the speed of sound in air at 20*C is 343#m/s#.
The density of air is 1.2041 #(kg)/m^3#.

#I=0.5^2/(2(1.2041)(343))=3.026588214271792*10^(-4)#
#3.03*10^(-4)W/m^2.#

I use my Physics for Scientists and Engineers (9th ed.) and my professor's notes to find equations and constants for most problems, including this one. Good luck!