The experimental setup used for the photoelectric effect is shown. It consists of an evacuated glass/quartz tube having a thin photosensitive plate C and another metal plate A. Light from the source S of sufficiently short wavelength passes through the window W and falls on the photosensitive plate C (emitter). The electrons are emitted by the plate C and are collected by the plate A (collector), by the electric field created by the battery. The battery maintains the potential difference between the plates C and A, that can be varied. Thus, the plate A can be maintained at a desired positive or negative potential with respect to emitter C. When the collector plate A is positive with respect to the emitter plate C, the electrons are attracted to it. The emission of electrons causes flow of electric current in the circuit called the photoelectric current.

The color of the light source should be ____ ?

Monochromatic

Monochromatic light source means that the frequency of the incident radiation is constant. In white light, there are mixed frequencies.