My last post said, "the simple answer is...."
So what's the more "complex" answer? Dunid to worry abt tis more complex answer if u r still not too familiar with the more basic concepts... so here goes...
In fact, freqency can affect the photoelectric current.... but why?
Each electron on the metal requires a different amt of energy (from a min value called to work function to extremely high value) to release it, so not every photon can release an electron, it is a probability thing. In fact, for every electron to be released, many many photons might be required, and exactly how many will depend on factors such as the type of metal involved, the frequency of the EM radiation, and even physical conditions such as temperature.
An electron can only be released from the metal if it so happens that the photon that hits a particular electron has energy at least equal to that required to release it. With higher frequency, the energy of each photon would be higher, so the chance that the electrons can meet with a photon with sufficient energy to release it would be higher, so statistically there will be a greater number of photoelectrons released per unit time. If that is the case, the current would also be higher.
Note: the frequency range might not be very large to give rise to a very significant change in the photoelectric current. in other words, the photoelectric current might not be affected much in practice.
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Just to add a wee bit more =)
In actual experimental conditions there's a finite bandwidth (ie spread of frequencies) even to such supposedly monochromatic light sources like lasers but even if one discounts the finite linewidths there will still be other sources of variation in the energies of the photons.
(Incidentally, maybe not for laser light sources but one way of reducing the line widths of light sources is to use a diffraction grating to select very precise frequencies, since you have stuff like d sin(theta) = n(lambda) which allows a fine control of the wavelenghth of light reflected off specific angles of the grating. Hehz ... so you see diffraction is not something that exists only in your physics lecture notes but is also useful for something =) ).
Anyway, yeah even if you have a monochromatic light source the frequency of the photon that reaches an electron is still subject to some variations - it's actually possible for a photon to scatter off atoms in the crystal lattice of the metal and impart energy and momentum to the crystal lattice. It's also possible for the vibrations of the crystal lattice to impart energy to the photon and increase its frequency.
The momentum of the crystal lattice appears in the form of the vibration of the crystal lattice; the physically relevant wavelengths of the crystal lattice vibrations in turn are governed by the inter-atomic spacing in the crystal lattice. If I remember correctly one of the main points which they had wanted to make at A level qunatum physics (at least during my time) is that energy in quantum mechanical systems is quantised and the energies of the vibrations are quantised as well. (This appears at the A level syllabus as the discrete absorption and emission spectrum.)
But that much said, the change in the frequency of the photons caused by lattice vibrations is still rather small lah so it's not really a very important effect as far as the photoelectric effect is concerned.
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