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: Wavelenght of the incident light

  1. May 19, 2008 #1
    1. The problem statement, all variables and given/known data
    An incident light shines on a mercury metal plate with a work function of -4.5 eV. The stopping voltage is observed to be -1.65 volts. What is the wavelenght of the incident light?


    2. Relevant equations
    wavelength=hc/E-0(it's a Greek sign n i dont have it in my computer)


    3. The attempt at a solution
    (4.14 X 10^-15 eVs) (3 X 10^8 m/s) / 1.65 + 4.5 = 1.242 X 10^-6 / 6.15

    1.242(10^2)/6.15 = 20.1954

    but the right answer is 201.7561 nm


    so can anyone please tell me what did I do wrong?
     
  2. jcsd
  3. May 19, 2008 #2

    rock.freak667

    User Avatar
    Homework Helper

    [tex]\frac{hc}{\lambda}=\phi +eV_s[/tex]

    Did you use the correct value for h in eV?
     
  4. May 19, 2008 #3
    i used h=4.14 X 10^ -15 am i supposed to use the other one? h=6.626 X 10^-34 ?
     
  5. May 19, 2008 #4

    rock.freak667

    User Avatar
    Homework Helper

    How'd you go from 1.242 X 10^-6 / 6.15 to 1.242(10^2)/6.15 = 20.1954?

    Because if you work out 1.242 X 10^-6 / 6.15 you'd get your answer.
     
  6. May 19, 2008 #5
    I was following one of the examples that my teacher did in class.

    well if i do 1.242 X 10^-6 / 6.15...it equals 2.01951 but the right answer is 201.7561 nm
     
  7. May 19, 2008 #6

    rock.freak667

    User Avatar
    Homework Helper

    1.242 X 10^-6 / 6.15 =201nm
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook