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: Photo electric effect problem

  1. May 21, 2015 #1
    1. The problem statement, all variables and given/known data
    A magnesium surface has a work.func of 3.68eV. El.mag. waves with wavelenght of 215nm strike the surface and eject electrons. Find the max Ek of the ejected electrons in eV.

    2. Relevant equations
    E=Ek-W <=> Ek=(hc/lambda) - W

    3. The attempt at a solution
    I convert eV to J and nm to m but i get -3.68*10^10eV, but the answer is suppoused to be 2.10eV.
    I even re did it but got the same answer, where em I going wrong?

    Thanks
     
  2. jcsd
  3. May 21, 2015 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    Hello.
    In order to see where you are going wrong, we need to see your entire calculation.
     
  4. May 21, 2015 #3
    Ek=(hc/lambda)-W

    ((6.63*10^-34)*(3*10^8))/(2.15*10^-7) - (5.888*10^-9)

    (9.25*10^-19) - ( (5.888*10^-9) = -5.887*10^-9 J / (1.6*10^-19) = -3.68*10^10eV
     
  5. May 21, 2015 #4

    TSny

    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    Check the power of 10 for the work function expressed in Joules.
     
  6. May 21, 2015 #5
    ah ye, there we go. thanks :)
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted