1. Not finding help here? Sign up for a free 30min 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!

Photons and the Photoelectric Effect

  1. Oct 28, 2006 #1
    Light is incident on the surface of metallic sodium, whose work function is 2.3 eV. The maximum speed of the photoelectrons emitted by the surface is 1.26e6 m/s. What is the wavelength of the light?

    I first converted Work Function to Joules:

    2.3eV x (1.6e-19 J / 1eV) = 3.68e-19 J

    The equation I know is:

    hf = KEmax + Work Function

    hf can also be written as:

    hc/lamda

    I thought I would substitute c w/ the 1.26e6 m/s and use KEmax as zero. My answer was 2.27e-9m and that is not correct.

    I used the following:

    f = Work Function / h = 5.55e14 Hz

    Then I used:

    lamda = v/f = 2.27e-9 m

    If I can't substitute v for c, then what am I looking for with v??? I have looked at this problem for 3 days w/ no new ideas. Anyone else have any?

    Thank you!!
     
  2. jcsd
  3. Oct 28, 2006 #2

    rsk

    User Avatar

    Have you worked out the ke of the electrons?

    When I do this I get the E for the light different to the value you give.

    And I don't understand what you're doing with this
    Find the Ke of the electron (joules) Convert WF to joules and add. This is the energy of the light.

    Then use E = hc/lamda

    I get 636 nm
     
  4. Oct 28, 2006 #3
    Thank you.

    I didn't realize I could find KE by using .5 *mv^2 and use the mass of an electron. Once I did that I added WF and then divied hc by my answer. The answer I got was 1.82e-7 m and that was correct.

    Thank you again for the help. I knew I was thinkging too hard and not looking at the obvious.
     
  5. Oct 29, 2006 #4

    rsk

    User Avatar

    good - don't know why my answer's wrong....one too many glases of wine before using a calculator?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Photons and the Photoelectric Effect
  1. Photoelectric effect (Replies: 6)

Loading...