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Molecular interpretation of temperature

  1. Aug 20, 2012 #1
    i'm trying to do my ap physics summer work, but i've been having a hard time trying to teach this to myself. i do really well in class, but i need a little bit of guidance to help explain how to use the equations the right way.

    i'm currently stuck on a question about vrms an it's relation to temp.

    1. The problem statement, all variables and given/known data
    the rms speed of molecules in a gas at 20degrees celsius is to be raised by 1%. To what temperature must it be raised?

    2. Relevant equations
    vrms= √3kT/m

    3. The attempt at a solution
    i don't have any clue where to start if it didn't give me the gas to find it's mass.


    -i was wondering if i could find someone who could maybe stay in touch for a day or two so i can reach out if i get stuck on anything
     
    Last edited: Aug 20, 2012
  2. jcsd
  3. Aug 20, 2012 #2
    What happens to constants when you need a ratio?
     
  4. Aug 20, 2012 #3
    okay, the temperature would change by sqrt 2, right ?
    essentially about 6 degrees kelvin.

    i'm stuck on another problem, it seems to be more conceptual.
    it says to prove how
    vrms=√P/ρ
    P, pressure
    ρ, density of the gas

    i started with the two equations
    P=1/3Nmv^2/V
    v^2=3KT/m

    i assumed the goal was to get the V from the first equation into the denominator of the second to try to get the density (m/v)
    some how all i've gotten to was
    P/ρ=[3KT(1/3)N]/m

    i'm trying to see if i can get the original 3KT/m to revert back to v^2, but i don't know how to get rid of the (1/3)N/m
     
  5. Aug 20, 2012 #4

    I like Serena

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    Welcome to PF, thattgirljoyy! :smile:

    It's not too far off 6 degrees... but there is no sqrt 2 involved that I can see... :confused:

    Let's put it in formulas:
    Before you have some unknown vrms,before at 20 degrees Celsius, or 393 K.
    Afterward you have vrms,after=1.01vrms,before at some unknown temperature T.
    Substitute and solve for T?


    Did you consider that m is the mass of one molecule?
    What is the mass of all molecules in the volume V?
     
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