Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ehrenfest's Theorem

  1. Jan 21, 2004 #1
    I have been asked to "find a solution to Ehrenfest's Theorem" (in this case for the expectation value of position, of a particle confined to a circle). What does this mean - what kind of answer should i find?
  2. jcsd
  3. Jan 22, 2004 #2
    Last edited by a moderator: May 1, 2017
  4. Jan 22, 2004 #3
    Thankyou, I have searched many times on google and other search engines, and have found (as on the websites you have shown me) that

    m*(d^2/dt^2)<x> = <F>

    which is a result of the form that I am looking for. But instead of <x> I have <exp(I*theta)>, so a function of theta, as I am interested in a particle confined to a circle. I have not been able to find out whether or not I can still use this same equation (despite my <exp(I*theta)> not being a linear variable like <x>). Please understand my problems with this; I am not trying to get someone else to do my homework for me - if you have never found it hard to do your 'homework', then you are very lucky.
  5. Jan 22, 2004 #4
    I don't remember all the details, but I thought for a potential proportional to r^2, you should expect out the classical value for such quantities as force and energy. You might want to try finding the classical value of the force for a particle confined to a circle using classical lagrangian mechanics, I don't think its that hard, and compare this answer to the quantum ananlog. Just an idea.
  6. Jan 25, 2004 #5

    Thanks spdf13,
    I've tried what you said and I think it has worked...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook