Further, we should note that in the wave picture, the absorption of
energy by electron takes place continuously over the entire
wavefront of the radiation Since a large number of electrons absorb energy,
the energy absorbed per electron per unit time turns out to be small Explicit calculations estimate that it can take hours or more for a single
electron to pick up sufficient energy to overcome the work function and
come out of the metal This conclusion is again in striking contrast to
observation (iv) that the photoelectric emission is instantaneous