With reference to the photoelectric effect, state what is meant by the threshold frequency.
Electromagnetic radiation of wavelength 
is incident on a metal surface. Electrons of maximum kinetic energy 
are emitted.
On the figure below, sketch the variation with 
of .
State an equation relating the gradient of the graph drawn on the figure above to the Planck constant 
. Explain any symbols you use.
Explain why, for any particular wavelength of electromagnetic radiation, most of the electrons are emitted with kinetic energies less than the maximum value .
Light of a particular wavelength is incident on a metal surface and gives rise to a photoelectric current. The wavelength is reduced. The intensity of the light is kept constant. State and explain the effect, if any, on the photoelectric current.
is the speed of light.
