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De Broglie Wavelength?

  1. Apr 24, 2012 #1
    I'm reviewing for one of my final exam and I can't seem to figure out this problem:

    Find the Debroglie wavelength of an electron with a KE of 40 ev.

    I got an answer of 3.9 x 10^-10 m.

    I keep getting it wrong and I'm not sure what to do.
    Thanks in advance!
  2. jcsd
  3. Apr 24, 2012 #2


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  4. Apr 24, 2012 #3
    You should only be using two formulas. One involves KE in terms of momentum and mass, and the other relates momentum and wavelength. Your answer is off by a factor of 1/2 so I'm guessing that you are making some mistake in your math.

    So why don't you show us what you've done?
  5. Apr 24, 2012 #4
    Hmm according to the hyperphysics website, my answer should have been
    1.85079 x 10 ^ -25

    would that be right?
    All i did was input the ev value of 40, but I did not input anything for mass or velocity.
  6. Apr 25, 2012 #5
    Why don't you show us your work? Your answer is not right yet, you were closer the first time. Mind you that this thread should be at the homework help section.
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