γCathodeAnodeeWhenlight strikes a polished (metal) surfaceelectrons are ejected.
Measurements were made of themaximum electron energy versus light frequencyand light
intensity. Classical physics predicted that the electron energy should increase with intensity, as the
electric field increases. This is not observed. The electron energy isindependent of intensity and
depends linearly on the light frequency, as seen the the figure above. The kinetic energy of the
electrons is given by Plank’s constant times the light frequency minusawork functionW which
depends on the material.
1
2
mv^2 =hν−W