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Homework Help: Estimate value for Planck's Constant? Please help hopeless A level student

  1. Sep 11, 2008 #1
    1. The problem statement, all variables and given/known data

    A clean surface of potassium in a vacuum is irradiated with light of wavelength 5.5 x10 -7 m and electrons are found just to emerge, but when light of wavelength 5.0 x 10 -7 m is incident, electrons emerge with energy 3.62 x 10-20 J. Estimate a value for Planck's constant.

    I understand the basics like finding work functions and Einstein's equation, but I haven't got a clue with this one. This is an emergency!
  2. jcsd
  3. Sep 11, 2008 #2
    Once the energy of the incident photons is sufficient to overcome the work function, any additional energy is converted into the KE of the electrons. The energy of a photon is E = hc/[tex]\lambda[/tex].

    We can therefore estimate h from the data you have by writing

    [tex]\Delta[/tex] E = h c / ([tex]\Delta[/tex][tex]\lambda[/tex]).

    Solve for h, and substitute your data.
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