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Most Probable Speed - Atoms From An Oven

  1. Jan 20, 2013 #1
    Hi there,

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

    Temp (T) is 900°C (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

  2. jcsd
  3. Jan 20, 2013 #2


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    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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