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 question

  1. Feb 5, 2012 #1
    1. The problem statement, all variables and given/known data
    What is the maximum kinetic energy (in eV) of a photoelectron emitted when a surface, whose work function is 5eV, is illuminated by photons whose wavelength is 400 nm
    1. -1.89
    2. 1.89
    3. 0
    4. 3.1

    2. Relevant equations
    hc/(lambda)=work function + KE max

    3. The attempt at a solution
    After plugging numbers in the formula above, I get KE max=-1.89 eV, but I guess I must have done something wrong, since energy cannot be negative.
  2. jcsd
  3. Feb 5, 2012 #2


    User Avatar
    Gold Member

    looks like your calculation is correct. Think about the physical significance.
  4. Feb 6, 2012 #3
    thank you, i've figured it out :)
    since lambda > lambda0, the photoelectric effect cannot occur, then KEmax = 0
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook