1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermal Conductivity

  1. May 28, 2007 #1
    1. The problem statement, all variables and given/known data
    The bulk phonon mean free path between phonon collisions for Umklapp process of a crystal is 30nm. If the crystal is of size 70nm, what is the effective mean free path that should be used in the equation for thermal conductivity?

    2. Relevant equations
    [tex]\kappa = \frac{1}{3}C_v\rho vl[/tex]

    3. The attempt at a solution
    I haven't got the foggiest clue for this one. My notes tell me that at low temperatures the mean free path is limited by the size of the sample, and that it is independent of temperature. However it doesn't mention anything about the effective mean free path. I know that l is the mean free path in the equation, and I would be tempted to say that l=30nm, but I'm pretty sure thats incorrect (even for a 1 mark example exam question that seems far too obvious).

    Any help on this would be appreciated.
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you help with the solution or looking for help too?
Draft saved Draft deleted

Similar Discussions: Thermal Conductivity
  1. Thermal Expansion (Replies: 0)