1. Limited time only! Sign up for a free 30min personal 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!

Wavelength of an electron homework

  1. Jun 9, 2009 #1
    1. The problem statement, all variables and given/known data

    -Electron has 3.00 MeV (or 4.8*10^-13 Joules)
    -it's relativistic
    -finding λ.

    2. Relevant equations


    λ=h/p (obviously)

    And I'm not sure if they're needed, but the relativistic eq's are:

    KE = mc^2/sqrt(1-(v/c)^2)
    p = mv/sqrt(1-(v/c)^2)

    I'm not sure if this one applies to relativistic speeds:

    E = hc/λ

    3. The attempt at a solution

    Attempt 1:

    E = hc/λ

    4.8E-13 = (6.63E-34)(3E8)/λ
    λ = (6.63E-34)(3E8)/(4.8E-13)
    λ = 4.14E-13 m

    BUT answer key says 3.58E-13

    If you could help, that would be great.
    Sorry if it's too long, and I'm a little unfamiliar with relativistic eqn's so forgive me if I screwed up on them.
  2. jcsd
  3. Jun 9, 2009 #2


    User Avatar
    Homework Helper

    The equation you used, [itex]E = hc/\lambda[/itex], only applies to photons (or massless particles in general). So you're not going to need that one here. If you're familiar with the equation
    [tex]E^2 = p^2c^2 + m^2c^4[/tex]
    I'd use that. If not, you can get the velocity from
    [tex]E = \frac{mc^2}{\sqrt{1 - v^2/c^2}}[/tex]
    (note that that's total energy, not kinetic energy) and compute the momentum from that.
  4. Jun 10, 2009 #3
    Thanks very much for the help.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Wavelength of an electron homework