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.

How does the stopping potential vary with the frequency of incident radiation?

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More the frequency of the incident radiation, more energetic are the photoelectrons and hence more retarding potential is required to stop them.