Light of wavelength 
is incident on a metal surface having a work function energy 
. Photoelectrons of maximum kinetic energy 
are emitted from the surface.
State an equation relating , and . Explain any other symbols you use.
The variation with 
of is shown in the figure below.
By reference to your answer in (a), explain why the gradient of the line does not depend on the metal surface.
The work function energy of sodium is 
. Determine the minimum wavelength 
at which is zero.
is the speed of light and 
is Planck constant.
, and 
.
