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!

Homework Help: X-ray Wavelengths

  1. Jul 25, 2008 #1
    1. The problem statement, all variables and given/known data
    The tube in a medical research X-ray unit uses lead (Z=82) as it's target. Assume the electrons are accelerated through the voltage calculated in part (b). What is the wavelength of the Kα line?

    2. Relevant equations
    KE=-13.6 ev ((Z-1)squared) / (1squared)

    3. The attempt at a solution
    KE=-13.6 ev ((Z-1)squared) / (1squared)
    KE =-13.6 ev ((82-1)squared)/ 1 squared)
    KE=89229.6 ev

    89229.6=(1.602E-19 J/ev)V
    V=89229.6 V

    E=(1.602E-19 C)(89229.6V)
    E=1.429E-14 J

    λ=((6.63E-34 J*s)(3E8 m/s))/(1.429E-14 J)
    λ=1.3856E-11 m = 0.013856 nm

    I'm not sure what's wrong... I correctly solved for KE and V, but I can't seem to solve for λ.
  2. jcsd
  3. Jul 25, 2008 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    I'm not sure where part b is, but think about the energies.

    The accelerated electron must have enough energy to dislodge a K-electron from the lead atom.

    Then another orbital electron will fall from a higher state to the spot in the K-shell, so the X-ray energy represents a difference in energy levels of atomic electrons. What's the significance of Kα?
  4. Jul 26, 2008 #3
    Oh okay I got it now. Thanks!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook