1.iii The Photoelectric Effect

When we shine light on a metal, electrons are emitted. The following facts were observed prior to 1905:

• If the frequency of radiation is below a cutoff frequency $\nu_0$ (where $\nu_0$ depends on the material) then no electrons are emitted.
• Regardless of the intensity, some electrons are emitted instantly after the light is turned on.
• Above $\nu_0$, the number of electrons emitted increases with intensity, but does not depend on frequency.
• The kinetic energy of each ejected electron increases linearly with frequency, but does not depend on intensity.