Kinetic THeory Question - !

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Kinetic THeory Question - URGENT!

Homework Statement



Ok so we've been asked to show that viscosity n = 1/3 p <v> lambda where lambda is the mean free path, p density of gas and <v> mean speed of particles in a gas

I've done this part..

Then the question says that in 1660 boyle did an experiment where he attached a pump to remove air from a vessel. it says that he found that there was no change in rate of damping when the pump was going.

This can be explained given the fact that n is independent of pressure, since lambda is inveresly proportional to density..

We're now asked to make a order of magnitude estimate of the lower limit to the pressure which boyle obtained (using reasonable assumptions about apparatus boyle may have used)

We're given that viscosity of air at atmostpheric pressure and at 293K is 18.2 x 10^-6 Ns/m^2


Homework Equations





The Attempt at a Solution



So i know that the approximation that viscosity is independent of pressure breaks down when lambda is comparable with the length of the container, call this D.

So assuming boyles container was 2m long, we can assume lambda was around 0.2m for his results to be pressure independent?

But then i dont know where to go..

I guess i can use the value of viscosity they've given, but how do i work out <v>?

thanks!
 

Answers and Replies

  • #2
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Average velocity of gas molecule is related to its kinetic energy.
Kinetic energy is related to temperature of gas.
The density may be found from
[tex]
PV=\frac{m}{\mu}RT

[/tex]
 

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