# Quick question on calculating wavelength.

1. Apr 10, 2010

### lyrebird

1. The problem statement, all variables and given/known data

Light strikes a sodium surface, causing photoelectric emission. The stopping potential for the ejected electrons is 4.6 V, and the work function of sodium is 2.2 eV. What is the wavelength of the incident light?

2. Relevant equations

3. The attempt at a solution

Problem solved, thanks. :)

Last edited: Apr 11, 2010
2. Apr 10, 2010

### Stonebridge

The equation E=hf for the energy of a photon of frequency f, will give energy in joules. (if h is in SI units)
So the work function and maximum ke of electrons (given by the stopping potential) also need to be in joules.

3. Apr 10, 2010

### lyrebird

To calculate the maximum kinetic energy, I would just multiply the charge on an electron by the stopping potential 4.6V, wouldn't I?

4. Apr 12, 2010

### Stonebridge

Yes. That's correct. It's the same idea as calculating the k.e. an electron gains when accelerating through a potential V. The only difference here is that the electric field acts to decelerate the electron rather than accelerate it.