Thus,
there exists a threshold frequency n0 (= f0/h) for the
metal surface, below which no photoelectric  emission
is possible, no matter how intense the incident
radiation may be or how long it falls on the surface ·
In this picture, intensity of radiation as noted above,
is proportional to the number of energy quanta per
unit area per unit time The greater the number of
energy quanta available, the greater is the number of
electrons absorbing the energy quanta  and greater,
therefore, is the number of electrons coming out of
the metal (for n > n0) This explains why, for n > n0,
photoelectric current is proportional to intensity