Let’s take a look at the experimental setup for studying the photoelectric effect.
At its most basic, we have two metal plates, called the emitter and the collector, housed in an evacuated tube. Outside the tube, the emitter and collector are connected through a micro-ammeter. When ultraviolet light is shone on the emitter plate, photoelectrons are liberated. Many of these photoelectrons will arrive at the collector, where they are reabsorbed. As photoelectrons are continuously liberated at the emitter and reabsorbed at the collector, the micro-ammeter records a continuous DC current, aka the photoelectric current.