A photo-cell employs photoelectric effect to convert

1. change in the intensity of illumination into a change in photoelectric current
2. change in the intensity of illumination into a change in the work function of the photo cathode
3. change in the frequency of light into a change in the electric current
4. change in the frequency of light into a change in electric voltage

A photo-cell employs photoelectric effect to convert light energy into photoelectric current.