Sound Intensity of a microphone

AI Thread Summary
The discussion focuses on calculating the sound intensity of a microphone with an area of 3.8 cm² that receives a sound energy of 4.2x10^-11 J over 2.87 seconds, resulting in an intensity of 3.85 x 10^-8 W/m². Participants express confusion regarding the calculations and the formulas used, particularly for determining the pressure variation in the sound wave. To find the pressure variation, the speed of sound (343 m/s) and air density (1.2 kg/m³) are relevant, with references to external articles for additional formulas. The conversation highlights the need for clarity on the relationship between sound intensity, energy density, and particle velocity. Overall, the thread emphasizes the importance of understanding the underlying physics concepts in sound intensity calculations.
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a) A microphone has an area of 3.8 cm^2. It receives during a 2.87 s time period a sound energy of 4.2x10-11 J. What is the intensity of the sound?

b) Using the intensity in the previous question, what is the variation of pressure in the sound wave if the speed of sound is 343 m/s and the density of air is 1.2 kg/m^3?

I determined part a) and got 3.85 x 10^-8 W/m^2, but I am not sure of any relevant equations to use for part b)...
 
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I don't see how you got 4.2x10-11 J. Formula?
Sound intensity has units of J per second per square meter, so you need to use the time and the area in meters squared.

I'm stumped on (b) and amazed that you are seeing this in physics 10.
There is an article on it in Wikipedia
http://en.wikipedia.org/wiki/Particle_velocity
but the pressure depends on the velocity of the particles of air.
The article on particle velocity
http://en.wikipedia.org/wiki/Particle_velocity#Equations_in_terms_of_other_measurements
has a formula for it in terms of the air density and the energy density of the wave. I suppose you could work all that out - you are given the area of the microphone and can find the length of the 2.87 second burst of sound . . .
 

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