A photocell employs photoelectric effect to convert

In a photoelectric effect when monochromatic radiations of suitable frequency fall on the photo_ sensitive plate called cathode, the photoelectrons are
emitted which get accelerated towards anode. These electrons flow in the outer circuit resulting in the photoelectric current.
Using the incident radiations of a fixed frequency, it is found that the photoelectric current increases linearly with the intensity of incident light as shown in the figure. Hence, a photocell employs photoelectric effect to convert change in the intensity of illumination into a change in photoelectric current.