1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Photoelectric Effect and ozone layer

  1. Oct 27, 2007 #1
    Hi. I hope someone can help. Here is the problem:

    [Pennies are made of zinc coated with copper. Copper has a work function of 4.7eV. The ozone layer blocks nearly all solar radiation with wavelength shorter than 320nm, but a very small amount of 200nm light still manages to reach the Earth's surface. Can direct sunlight produce photoelectrons from a penny?]

    I converted the 4.7eV into joules: 4.7eV * 1.602e-19J = 7.529e-19J
    I found the minimum kinetic energy needed to for the electrons to escape from the copper:
    KE = e * V_o => 1.602e-19 * 7.529e-19 = 1.206e-37J

    I'm thinking that I need to use the 200nm to find out whether the kinetic energy I calculated will be produced by the sunlight, but I don't see how to do that.
  2. jcsd
  3. Oct 27, 2007 #2

    Chi Meson

    User Avatar
    Science Advisor
    Homework Helper

    Your reasoning is incorrect. KE = E - W (E is energy per photon, W is work function, KE is max kinetic energy of photoelectron).

    Stay in eV, it's easier. Use 4.14 x 10^-15 eVs as h.

    Energy per photon is hf =hc/wavelength.

    How much energy in a 200 nm photon?
    Last edited: Oct 27, 2007
  4. Oct 27, 2007 #3
    Thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook