# Confused about the Photoelectric Effect?

If an incident photon with frequency f hits a metal with a work force of w: How do I find the color of the incident photon and the threshold frequency of the metal?

I missed out on the days in my physics class where they covered work force and stopping voltage, so what equations are necessary to find the color and threshold frequency?

I know this is probably an easy question, but if you could please show me the steps with an explanation, that would really help me prepare for my test on Monday.

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A quick google search, and wikipedia read would probably be quite fruitful. –  DilithiumMatrix Apr 28 '13 at 0:57
@zhermes - I've been searching for an hour and I have no idea how to find the frequency of metal, only the frequency of a photon. –  Genevieve Ccio Apr 28 '13 at 1:05
The very first article in a google search is wikipedia's photoelectric effect. The article defines a metal's threshold frequency within roughly the first page. –  DilithiumMatrix Apr 28 '13 at 1:16

## 1 Answer

I think you should re-read the question, because "frequency of the metal" doesn't make much sense in this context. And the color of photon is dependant only on it's frequency which is given. Do you need some further explanations on that?

Photoeffect's main equation is one of energy balance. The only energy source in this event is the photon whose energy is $hf$. If that is enough to eject an electron ($\ge w$), the emission occurs. The leftover energy becomes kinetic energy of the electron. $$hf=w+K$$

The threshold is the case where you get just enough energy to emit the electron but no leftover. The needed equation is $$hf=w$$

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I meant "threshold frequency of the metal" sorry. :( –  Genevieve Ccio Apr 27 '13 at 23:07
Also, to find the color, I needed to find the wavelength in nm. –  Genevieve Ccio Apr 28 '13 at 0:19
The equation for that is c/f = lambda –  Genevieve Ccio Apr 28 '13 at 0:20
So you're saying that to find the threshold frequency of the metal, you have to divide w/h? –  Genevieve Ccio Apr 28 '13 at 1:04
Yes, w/h is correct. –  Juris Apr 28 '13 at 10:58