W =hfo
gives the minimum energy required to remove a delocalised electron from the surface of the metal. W = work function, h = Plancks constant, fo = threshold frequency for the metal.
Kmax = h(f - fo)
gives max kinetic energy of ejected electrons. f greater than fo allows photoelectric effect to occur.
Source A with higher f will cause more electrons to have sufficient kinetic energy to overcome W.
The photons of a light beam have a characteristic energy proportional to the frequency of the light. In the photoemission process, if an electron within some material absorbs the energy of one photon and acquires more energy than the work function (the electron binding energy) of the material, it is ejected. If the photon energy is too low, the electron is unable to escape the material.
Increasing the intensity of the light beam increases the number of photons in the light beam, and thus increases the number of electrons excited, but does not increase the energy that each electron possesses.
The energy of the emitted electrons does not depend on the intensity of the incoming light, but only on the energy or frequency of the individual photons. It is an interaction between the incident photon and the outermost electron.