# Photoelectric effect and emission

How would I calculate the number of electrons emitted from say a given intensity of light. For instance number of electrons emitted per unit time interval (second) in a $$\text{mm}^2$$ metal surface? Furthermore we are given some probability of an electron being emitted for each photon.

For example: If I were to say the intensity of the light is $$I_0 \text{W}{m^-2}$$, and the probability of a photon emitting a photo electron is $$1$$ in $$400$$, how can we find the number of photo electrons released per second for each $$\text{mm}^2$$ metal surface?

My confusions: * how do we find the number of photons emitted by a given intensity of light? * to me it seems like this question is incomplete, or there is not enough information given.

• It is indeed incomplete because the light wavelength or frequency is missing. – Jasper Apr 14 at 8:45
• Say that we do know the frequency and wavelength how would we still do it then? We can only the energy of the light in that case, still dont know how to get number photons emitted – Aurora Borealis Apr 14 at 9:04
• @AuroraBorealis The intensity divided by the energy would give the number of photons striking the surface per second per unit area. – User Apr 14 at 10:05