Please show work. And thanks An electronic point source emits sound isotropicall
ID: 2244769 • Letter: P
Question
Please show work. And thanks
An electronic point source emits sound isotropically at a frequency of 2 Ý 103 Hz and a power of 30 watts. A small microphone has an area of 0.74 cm2 and is located 181 meters from the point source.
1) What is the sound intensity at the microphone?
I = _________ W/m^2
2) What is the power intercepted by the microphone?
Pin = __________ W
3) How many minutes will it take for the microphone to receive 0.1 Joules from this sound?
DeltaT = __________ min
4) What is the sound intensity level at the microphone from this point source?
B = ____________ dB
5) What would be the sound intensity level at the microphone if the point source doubled its power output?
B = _____________ dB
Explanation / Answer
1) I = power/Area = 30/(4*3.14*181^2) = 7.29*10^-5 W/m^2
2) Pin = I*A = 7.29*10^-5*0.74*10^-4 = 5.395*10^-9 watts
3) E = Pin*t
t = E/pin
= 1/5.395*10^-9
= 1.85357*10^8 s
= 3.0893*10^6 min
4)
B = 10dB*log(I/Io)
= 10 dB*log(7.29*10^-5/10^-12)
= 78.6 dB
5)
B = 10dB*log(2*I/Io)
= 10 dB*log(2*7.29*10^-5/10^-12)
= 81.64 dB