# Photoelectric effect, retarding potential

1. Oct 7, 2007

### howin

[SOLVED] Photoelectric effect, retarding potential

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

If the photocurrent of a photocell is cut off by a retarding potential of 0.92 volts for monochromatic radiation of 2500 A (A with the little circle above it), what is the work function of the material.

2. Relevant equations

My book and professor use different symbols so I am going to define the symbols I am using:
Ø means retarding potential / stopping potential
W means work function

e Ø = hc/lambda - W

hc = 1240 eV

3. The attempt at a solution

radiance is invariant with lambda b/c monochromatic
According to the graph of photocurrent i vs. anode voltage V, it is when V = -Ø that i goes to 0. I don't see where 2500A fits in, except that that must give me lambda so that I can solve for W in the equation above.

2. Oct 7, 2007

### HungryChemist

You've got everything you need. Just plug them all in to your equation and solve for W!

3. Oct 8, 2007

### Gokul43201

Staff Emeritus
$2500 \AA$ is the wavelength.

$$1 \AA = 10^{-10}m$$

4. Oct 8, 2007

### howin

Wow, that helps a lot!

Oh okay, having A be a measure of length helps a lot...I was an econ/poli sci major so missed a lot of this stuff undergrad = )

2500A = 2.5 * 10^-7m = 250 nm

So W = (1240 eV nm / 250 nm) - .92 eV = 4.04 eV which is the work function.

Thanks!