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Male Rana catesbeiana bullfrogs are known for their loud mating call. The call is emitted not by the frog’s mouth but by its eardrums, which lie on the surface of the head. And, surprisingly, the sound has nothing to do with the frog’s inflated throat. If the emitted sound has a frequency of 260Hzand a sound level of85dB(near the eardrum), what is the amplitude of the eardrum’s oscillation? The air density is1.21kg/m3.

Short Answer

Expert verified

The eardrum’s oscillations has the amplitude of 0.76 â¶Ä°Ó¾À.

Step by step solution

01

Given

  1. Frequency: f = 260 Hz
  2. Air density:ÒÏ=1.21 k²µ/³¾2
  3. Level of intensity:β=85 dµþ
02

Determining the concept

Find the sound intensity using the formula for the sound level in terms of intensity. Write the amplitude in terms of intensity, density, frequency and speed of sound.

Formulae are as follow:

β=10logII0

I=12ÒÏv(2Ï€´Ú)2A2

where, I,I0 are intensities, f is frequency, A is area,ÒÏ is density and v is density.

03

Determining the amplitude of the eardrum’s oscillation 

From the formula for sound level,

β=10logII0

I=I0100.1β=(10−12 W/³¾2)(108.5 dµþ)=3.162×10−4W/m2

Since, intensity of sound is defined as,

I=12ÒÏv(2Ï€´Ú)2A2

A=2IÒÏv(2Ï€´Ú)2=2×(3.162×10−4 W/m2)(1.21 â¶Ä‰k²µ/m3)(340″¾/s)(2×3.14×260 H³ú)2=0.76 â¶Ä°Ó¾À

Hence, the oscillations has the amplitude equal to0.76 â¶Ä°Ó¾À .

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