Most probable speed

Physics and electronics discussion, revision, exam and homework help.

Announcements Posted on
TSR launches Learn Together! - Our new subscription to help improve your learning 16-05-2013
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
Sign in to Reply
  1. danhirons's Avatar
    • Exalted and Worshipped Member
    • Location: Birmingham/Oxford
    • Posts: 1,038
    Most probable speed
    For a Nitrogen molecule I'm using the equation:

    sqrt(2KbT/m)

    The temp is at 500k and the boltzmann constant is obviously a constant value but I'm not sure what the m is, is it the molar mass in kg (if so I get a ridiculously small value for the speed) or is it the mass of one particle of N2 so 28 x10^-3 x (avogadro's constant) ??? But then I get a really big value which seems too large to be true


    EDIT: Also have a question about calculating the rms speed of free electrons in the sun's atmosphere. Though it gives me a value for the pressure so can I not just use the Vrms equation = sqrt(3KbT/m)???

    Thanks
    Dan
    Last edited by danhirons; 28-12-2010 at 22:22.
  2. danhirons's Avatar
    • Exalted and Worshipped Member
    • Location: Birmingham/Oxford
    • Posts: 1,038
    Re: Most probable speed
    Anyone? :P
  3. Morgan141's Avatar
    • Exalted and Worshipped Member
    • Location: Loughborough
    • Posts: 987
    Re: Most probable speed
    It is the mass of one nitrogen molecule. This can be approximated to 28amu ( total number of protons and neutrons x the atomic mass unit (~ 1.66x10^-27kg)).

    It should be rather large , they do move fairly quick!

    As for your edit I think the problem with using that equation lies with knowing the temperature, which I suspect you're not given. Do you know a relation between pressure and temperature?
    Last edited by Morgan141; 29-12-2010 at 16:44.
Sign in to Reply
Share this discussion:  
Article updates
Moderators

We have a brilliant team of more than 60 volunteers looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.