The photoelectric effect may be represented by the equation
.
State what is meant by work function energy.
The variation with frequency 
of the maximum kinetic energy 
of photoelectrons emitted from the surface of sodium metal is shown in the figure below.
Use the gradient of the graph in the figure above to determine a value for the Planck constant 
. Show your working.
The sodium metal in (b) has a work function energy of 
. The sodium is replaced by calcium, which has a work function energy of 
. On the figure above, draw a line to show the variation with frequency of the maximum kinetic energy of photoelectrons emitted from the surface of calcium.
.
