Physics Question Thank you!! and Problem 20.26 art The intensity level of a \"Su

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Physics Question

Thank you!!

and

Problem 20.26 art The intensity level of a "Super-Silent" power lawn mower at a distance of 1.0 m is 100 dB. You wake up one morning to find that four of your neighbors are all mowing their lawns using identical "Super-Silent" mowers. When they are each 20 m from your open bedroom window, what is the intensity level of the sound in your bedroom? You can neglect any absorption, reflection, or interference of the sound. The lowest detectable intensity is 1.010-12 Wm2 104 dB 50 dB O 40 dB O 80 dB 80 dB 400 dB

Explanation / Answer

A. Power/Area = intensity
given, Intensity = 100db = 10log(I/10^-12)
10 = log(I/10^-12)
10^10*10^-12 = I
I = 0.01 = P/4*pi*1^2
P = 0.01*4pi
  
For other case, P/A = I'
I' = 0.01*4*pi/4*pi*20^2 = 1/40000
in decibel scale, 10log(1/40000*10^-12) = 74 dB (apx 80 dB nearest value)
B. Distance from the centre to the speaker = 2.5 m
let the user move distance x
Path difference in the waves from speaker = 2.5 + x - (2.5 - x) = 2x
for dwestructive intereference, 2x = lambda/2 = 344/875*2
x = 9.828 cm

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