To study the photoelectric effect, the collector plate in the vacuum tube is made negative with respect to the emitter plate.

To study the photoelectric effect, the collector plate in the vacuum tube is made negative with respect to the emitter plate. Thus, the collecting surface will repel electrons coming from the emitter plate and only those electrons with enough energy to overcome this force will arrive at the collector plate and register a current in the ammeter. When the applied potential difference is large enough to repel the highest kinetic energy electrons ejected by light at a given frequency (i.e., the electrons ejected from the topmost layer of the metal),the detected current will reach zero. The minimum voltage where this occurs is identified as the cutoff voltage,V0.

Using conservation of energy,show that V0= (h/e)ν−φ

Here,e is the charge of the electron,h is Planck's constant,ν is the highest frequency striking the emitter plate, and φ (oreφ, depending on your definition) is the "workfunction" of the emitter plate. Notice that this equation yields a linear relationship ("y = mx + b") between the stopping voltage (V0) and the frequency of light, (ν) striking the emitter plate. This simple expression allows us to determine the work-function with a handheld multimeter