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

1 Answer
Sarah M
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 343m/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!

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