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

Homework Help: Finding wavelength of an electron

  1. Jun 30, 2011 #1
    1. The problem statement, all variables and given/known data
    What is the wavelength of an electron with a kinetic energy of 2.00 MeV?

    What is the wavelength of an electron with a kinetic energy of 2.08 GeV?

    (Possibly useful constants: hc = 1239.8 eVnm, rest energy of the electron: E0,e = 511.0 keV.)


    2. Relevant equations
    [itex]\lambda[/itex]=hc/(2(mc2)K)1/2



    3. The attempt at a solution
    Should be pretty straightforward, I keep getting the wrong answer though, should just be plug and chug, i would think.
     
  2. jcsd
  3. Jun 30, 2011 #2
    Are you sure that's a correct equation for the de Broglie wavelength? I've never seen it written that way, though I guess the units do check out...Making sure to put everything in the same units?

    I did a rough calculation and you're right, the answers don't seem realistic.
     
    Last edited: Jun 30, 2011
  4. Jun 30, 2011 #3

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    Your equation for the wavelength is for a non-relativistic electron. Those kinetic energies, however, are greater than the rest energy of the electron, so you're in the relativistic regime.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook