3)
Equation (11 3) shows that the greater the work
function f0, the higher the minimum or threshold
frequency n0 needed to emit photoelectrons 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