For a particular metal surface, it is observed that there is a minimum frequency of light below which photoelectric emission does not occur. This observation provides evidence for a particulate nature of electromagnetic radiation.
State three further observations from photoelectric emission that provide evidence for a particulate nature of electromagnetic radiation.
Some data for the variation with frequency 
of the maximum kinetic energy 
of electrons emitted from a metal surface are shown in the graph below.
Explain why emitted electrons may have kinetic energy less than the maximum at any particular frequency.
Use the graph above to determine
the threshold frequency,
the work function energy, in 
, of the metal surface.
.
.
