Question

In an experiment on the photoelectric effect, a certain frequency of light produces emissions from a metal. Which observation is also possible in this experiment?
A. Lower frequency light causes more electron emissions.
B. Lower frequency light causes no electron emissions.
C. Higher frequency light has no effect on electron emissions.
D, Higher frequency light causes no electron emissions.

Answer 1

The frequency of a light wave is directly related to its energy (i.e. the higher the frequency, the higher the energy of the photons). So, when light of a certain frequency is incident on a metal, it must have a certain energy to overcome the work function of the metal in order to emit an electron. The work function is the energy required to promote an electron from its ground state in an atom of the metal into an excited state at n = infinity, where it will be ejected from the surface. So:

A: If the lower frequency of light is below the work function of the metal (a characteristic value for a given metal), then no electrons will be emitted. So, it would definitely not cause more electron emissions.
(B): Again, if the original light energy was directly at the work function of the metal (leading to electrons being emitted with no kinetic/excess energy), then a lower frequency would lead to no emission.
C: The higher frequency of light won't effect the number of electrons being emitted, but will effect their kinetic energy, as any excess energy which the photons of light had above the required work function is converted into the kinetic energy of the emitted electrons.
D: Clearly, higher frequency emission would still be higher than the work function, and electron emissions would still occur.

So overall I'd say that (B.) is the possible observation during the experiment.

Answer 2

Its a 1 to 1 interaction. \[E = Hf\] where E is the amount of energy needed to emit the electron from the metal. H is Plancks constant that stays the same. This means if f (frequency) is too low or small, the electron will not have enough energy to be emitted. So according to the equation (B) must be true.