A photoelectric cell is a remarkable device used to accurately measure the intensity of light. It operates by efficiently converting incident or reaching light into an electric current, which can then be precisely measured. Photometers for various applications extensively utilize this ingenious invention. A photometer is an electronic device consisting of layers of special materials capable of converting light directly into electricity.
This electronic device converts light to electricity and is also known as a photo tube or electric eye. The process of photoelectricity occurs through three distinct yet apparently similar methods: photoconductive, photoemissive, and photovoltaic effects. A photoelectric cell works on the principle of photoelectric effect.
Photoelectric Effect
Albert Einstein (1879–1955) was the one who provided the explanation. He showed that a light beam hitting objects, like a piece of metal, can be thought of as a stream of moving particles called photons. The photons transfer their energy to atoms in the metal, causing some electrons to be knocked out and generating an electric current.
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Photoelectric Cell Working
When the light of greater frequency, particularly more than the threshold frequency, falls on the cathode, it leads to the emission of photoelectrons. These electrons are attracted by the anode as it is connected to the positive terminal of the battery. This leads to the flow of current.
But, as soon as the light is cut off, there is no emission of photoelectrons from the cathode. Thus, there is no current in the external circuit.
Photoelectric Cell Applications
Here is a list of applications where these cells are used.
- Photoelectric cells are used for reproducing sound from movie films.
- Commonly used in counting devices to keep track of the number of people entering a hall, as long as they enter one by one.
- Used in burglar and fire alarms.
- Photocells are used in street light circuits to automatically turn the lights on and off at dusk and dawn.
- In photometry, they are employed to compare the illuminating capacities of two light sources.
- In public buildings to automatically open the doors
- For the determination of Planck’s Constant
- Photoelectric cells are used in television cameras to capture and transmit scenes.
- They are also used in photo telegraphy to transmit pictures, prints, etc. via radio or telegraphy.
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