Finding the wave length incident light troubles! wee!

1. Apr 15, 2006

mr_coffee

hello everyone!
I'm having some troubles figuring out what i'm doing wrong here.
The problem says:
Light strikes a sodium surface, causing photoelectric emission. The stopping potential for the ejected electrons is 6.1 V, and the work function of sodium is 2.2 eV. What is the wavelength of the incident light?
it wants the answer in nm as well, i submitted:
2.39277E-17 nm which was wrong

Here is how i got that answer:
let f equal frequencey;
let L = wave length;
h is planks constant which is:
6.62E-34 Js
f = (6.1 + 2.2)/h;
f = 1.25E34;
L = c/f, where c is the speed of light.
c = 3E8 m/s;

I figured out the fequencey so:
L = 3E8/(1.25E34);
L = 2.39277E-26m;
it wants it in nano meters so i divided it by E-9;
L = 2.39277E-17 nm;

Any ideas where i screwed up? Thanks!

I'm thinking its wrong because the 2.2 units are eV, not V. I know 1eV = 1.6E-19J, but that would just convert 2.2 into jouls, not volts.

EDIT:
I got it, i just had to convert planks constant to eVs instead of Js.

Last edited: Apr 15, 2006