By reference to the photoelectric effect, explain what is meant by work function energy.
In an experiment, electromagnetic radiation of frequency 
is incident on a metal surface. The results in the figure below show the variation with frequency of the maximum kinetic energy 
of electrons emitted from the surface.
Determine the work function energy in 
of the metal used in the experiment.
The work function energy in 
for some metals is given in the table below.
Determine the metal used in the experiment. Show your working.
The intensity of the electromagnetic radiation for one particular frequency in (b) is increased. State and explain the change, if any, in:
the maximum kinetic energy of the emitted electrons
the rate of emission of photoelectrons.
.
, so the metal used in the experiment is potassium.
