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-   -   Most Probable Speed - Atoms From An Oven (http://www.physicsforums.com/showthread.php?t=665625)

bobbles22 Jan20-13 04:00 PM

Most Probable Speed - Atoms From An Oven
 
Hi there,

I'm looking to find the most probable speed of atoms ejected from an oven.

Temp (T) is 900C (so 1173.15K).

The material is aluminium with molar mass 0.027kg mol-1

I've got the formula vmp=√(2kT/m)

I'm fine with everything above, but I'm not sure what value to use as the Boltzmann constant k.

Can anyone please help me here? Do I have the right equation and what value for the constant should I use (sounds silly, but it changes depending upon units. I've tried a couple but get silly tiny speeds out. I think I should expect something in the region of a few hundred metres per second).

Many thanks

Bob

AlephZero Jan20-13 04:37 PM

Re: Most Probable Speed - Atoms From An Oven
 
In SI units:
K = 1.38e-23 J/K
m = mass of one molecule = 0.027/6.022e23 kg
T = 1173 K

... which gives a velocity of "hundreds of m/s" as you expected.


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