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Homework Help: An electron traveling at a speed of

  1. Aug 1, 2010 #1
    1. The problem statement, all variables and given/known data
    An electron traveling at a speed of 6.0 x10^7 m/s. strikes the target of an x-ray tube. Upon impact, the electron decelerates to 1/4th of its original speed, emitting an x-ray in the process. What is the wavelength of the x-ray photon?

    2. Relevant equations
    I think I'm suppose to use the formula E=hf (eqn 1) and v=lambda*f (eqn 2)

    3. The attempt at a solution
    I manipulated both equations (eqn 1 and eqn 2) to get the formula E=(h*v)/(lambda), but that leaves me with two unknowns..when all I want is lambda to be the only unknown. I'm not sure how I would find the energy...and I'm not sure if I'm even using the correct formulas. Hopefully I'm on the right track???
  2. jcsd
  3. Aug 1, 2010 #2
    What you want is the wavelength of the X-ray - an EM wave. What is its speed ?
  4. Aug 2, 2010 #3
    we can find the wavelength of the emitted x-ray photon. using

    first find the kinetic energy of the electron using K.E = 1/2 m*v^2.
    then apply the formula

    lambda = (h*v)/K.E

    it will give the answer for you.
  5. Aug 2, 2010 #4


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    Staff: Mentor

    That is incorrect. Even a dimensional analysis shows that there is something wrong with that equation.

    And please do not do the original poster's (OP's) work for them -- they are required to do the work themselves. You may provide hints and ask questions, in order to help them figure out the problem on their own.
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