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Briefly describe two phenomena associated with the photoelectric effect that cannot be explained using a wave theory of light.
The maximum energy 
of electrons emitted from a metal surface when illuminated by light of wavelength 
is given by the expression
where 
is the Planck constant and 
is the speed of light.
Identify the symbol 
.
The variation with 
of for the metal surface is shown in the graph below.
Use the graph above to determine the magnitude of .
Use the gradient of the graph above to determine a value for the Planck constant .
The metal surface in (b) becomes oxidised. Photoelectric emission is still observed but the work function energy is increased. On the graph above, draw a line to show the variation with of for the oxidised surface.
or 
.
.
