Photoelectric effect is the phenomenon in which electrons are emitted from a material when light of a certain frequency or higher is shone on it. This effect is used in various applications, some of which are:

Photocell
- A photocell is a device that converts light energy into electrical energy using the photoelectric effect. It consists of a metal plate coated with a photosensitive material, such as caesium or potassium, and a second metal plate called the collector. When light falls on the photosensitive material, electrons are emitted and attracted to the collector, creating a flow of current. Photocells are used in light meters, solar cells, and other light-sensitive applications.

Sonar
- Sonar (Sound Navigation and Ranging) is a technique used to locate objects underwater by emitting sound waves and measuring the time it takes for them to bounce back. The photoelectric effect is used in the transducers that convert electrical signals into sound waves and vice versa. These transducers use piezoelectric materials that emit light when subjected to pressure, which in turn causes electrons to be emitted due to the photoelectric effect. This creates an electrical signal that can be used to detect the distance and location of objects underwater.

Electron Microscope
- An electron microscope is a type of microscope that uses a beam of electrons instead of light to magnify objects. The photoelectric effect is used to generate the electrons in the electron gun of the microscope. A heated filament emits electrons through the photoelectric effect, which are then accelerated and focused into a beam by electromagnetic fields. This beam is then used to scan the object being observed, creating a highly magnified image.

Optical fibers
- Optical fibers are thin strands of glass or plastic that are used to transmit light signals over long distances. The photoelectric effect is used in the detectors that convert the light signals back into electrical signals at the receiving end of the fiber. These detectors use materials that emit electrons when exposed to light, creating an electrical signal that can be transmitted over a wire or wireless connection.

In conclusion, the photoelectric effect is a phenomenon that has a wide range of applications in various fields, from converting light energy into electrical energy to detecting objects underwater and magnifying objects at the microscopic level.