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Photoelectric Effect

  1. Nov 22, 2009 #1
    1. The problem statement, all variables and given/known data

    The work function of chromium metal is 7.2 x 10-19 J. What is the maximum speed an electron can be moving if it is ejected from chromium metal by light of wavelength 250 nm? (Answer: u= 4 x105 m/s)

    2. Relevant equations

    [tex]\Phi = h v_{0}[/tex]

    [tex]KE = h v_{light} - \Phi = \frac{m_{e} u^{2}_{e}}{2}[/tex]

    [tex]\Delta E_{light}= \Phi + KE[/tex]

    [tex]h[/tex] is Planck's constant
    [tex]v_{0}[/tex] is the characteristic frequency
    [tex]m_e[/tex] is the mass of an electron (9.1 x 10-31 kg)
    [tex]u_e[/tex] is the speed of the electron

    3. The attempt at a solution

    [tex]7.2\times10^{-19} J = \frac{(9.1\times10^{-31} kg) (u^{2}_{e})}{2}[/tex]

    [tex]u_e \approx 1.3 \times 10^6 m/s[/tex]
    Last edited: Nov 22, 2009
  2. jcsd
  3. Nov 27, 2009 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Keep this equation in mind.

    You have left out the energy of the photon, the hvlight in your earlier equation.
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