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Homework Help: Interactions of Light and Matter

  1. Oct 2, 2009 #1
    1. The problem statement, all variables and given/known data
    The tungsten cathode in an electron microscope has a work function of 4.5 eV and is heated to release electrons that are initially at rest (near the cathode). The electrons are accelerated by a potential difference that creates a beam with a de Broglie wavelength of 0.040 nm.

    Calculate the kinetic energy, in Joules, of an electron in the beam.

    2. Relevant equations
    Ek = hf - w

    F = c / [tex]\lambda[/tex]

    3. The attempt at a solution
    Ek = hf - w
    F = c / [tex]\lambda[/tex]
    Therefore, Ek = h x (c/[tex]\lambda[/tex]) - w
    Ek = 6.63 x 10^-34 x (3 x 10^8/0.040 x 10^-9) - 4.5
    Ek = -4.5?
    Feel like im doing something very wrong here...
  2. jcsd
  3. Oct 2, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    How does the de Broglie wavelength relate to the particle's momentum?
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