Question

A point source emits 30.0 W of sound isotropically (in all directions). A small microphone with an area of 0.750 cm² is located 200 m away from the source.

(a) Find the sound intensity at the location of the microphone in W/m² .

(b) Find the power intercepted by the microphone.

(c) Find the displacement amplitude s_m of the sound wave at the position of the microphone taking the frequency of the sound to be 50.0 Hz.

Answer 1

(a) I = P/A

I = 30 / 4pi*200²

I = 5.97e-5 W/m²

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(b) P = IA

P = 5.97e-5 * 7.5e-5

P = 4.48e-9 W

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(c) For this part, I need to know velocity and density

the relation between displacement amplitude and intensity is

d = I / 2² * density * velocity * frequency²