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Question: At what frequency would the wavelength of sound in air be equal to the mean free path of oxygen molecules at 1 atmpressure and 0.00 0C? The molecular diameter is3.0×10-8cm.

Short Answer

Expert verified

Answer

The required value of frequency is3.5×109Hz .

Step by step solution

01

Given data

  • Temperature;

T=0.00°C=273.15K

  • Pressure;

p=1.0atm=1.01×105Pa

  • Molecular diameter;

d=3.0×10-8cm=3.0×10-10m

02

Understanding the concept

The expression for the velocity of sound is given by,

v=fλ

Here v is the velocity of the sound, F is the frequency,λ is the wavelength.

03

Calculate the frequency at which wavelength of sound in air would be equal to the mean free path of oxygen molecules at 1 atm pressure and 0.00 0C

L=λ

From the above expression,

,v=fλ

Substitute for into the above equation,

f=331λ

Let the mean free path of oxygen molecules be L ,

Given condition is

L=λ

Hence,

f=331L

But,L=12Ï€d2NV

Also, according to the gas law,

NV=pkT

Therefore,

f=33112Ï€d2pkT

Substitute 3.0×10-10mfor d , 1.01×105Pa for p , 1.38×10-23 J/molecule ·Kfor k and273.15 K for T into the above equation.

f=331123.142(3.0×10-10)21.01×1051.38×10-23273.15=3.54×109≈3.5×109Hz

Therefore, the required value of frequency is3.5×109Hz .

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