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 threshold

  1. Oct 13, 2014 #1
    When a cm thick surface is illuminated with light of wavelength lambda,the stopping potential is V. When the same surface is illuminated by light of wavelength 2lambda , the stopping potential is V/3.The threshold wavelength for the surface is ?

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Oct 13, 2014 #2


    User Avatar
    Science Advisor
    Gold Member

    Did you try to do this problem yourself?
  4. Oct 14, 2014 #3
    Yes i tried but i am unable to solve it.
  5. Oct 14, 2014 #4


    User Avatar

    Staff: Mentor

    Hi Nairabhi. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    What equations do you have that you'll use here?
    Last edited by a moderator: May 7, 2017
  6. Oct 14, 2014 #5
    See according to Einstein equation KE(Max)= Energy of photons - work function of surface, but since work function is not given i have assumed it
    to be 0. And energy of photons is equal to hc/lamda and this energy is equal to KE(Max) or the stopping potential so using these equations and i am trying to find a relation between them and find the threshold wavelength .However i don't understand what role does the thickness of surface plays which is 1cm ?
    Last edited by a moderator: May 7, 2017
  7. Oct 14, 2014 #6


    User Avatar

    Staff: Mentor

    You should assume work function is non-zero, and is fixed at some value.

    That material thickness may simply mean "of suitable thickness" for our purposes.

    Does the textbook give the correct answer?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted