A photocell is a vacuum tube with a concave cathode called an emitter, made from a material that emits electrons easily. When light of a frequency greater than the threshold frequency, shines on the emitter, electrons are released. The concave emitter focuses electrons on a thin wire anode called a collector. The thin anode does not block light. When the collector is at a positve potential, electrons are attracted to it.
The photocell is at the centre of
the many applications of the photoelectric effect. It consists of a
curved emitter and a rod as collector, so as not to inhibit light from
reaching the emitter.
The structure of a typical photocell is shown below:
The flash of a camera uses the photoelectric effect
(for the source of this image and for more information click
here)
Photocells are used in medicine. An example is
shown in the diagram below:
Photocells are used in garage
door openers.
An example is shown in the diagram below:
Photocells are used in movie film. An example is shown in the diagram below: