It is a device used to convert light energy into electrical energy. It is also called electric eye. It is of three types-
Photoemissive cell.
Photovoltaic cell.
Photoconductive cell.
Photoemissive cell:
It consists of an evacuated glass or quartz tube in which two electrodes, cathode (C) and anode (A) are fitted. A high tension battery ‘B’ and resistance ‘R’ are connected between cathode and anode.
When light is incident on cathode, it emits photo electrons, which are attracted by anode. Hence photoelectric current flows through circuit. The photoelectric current is very small, therefore, it is to be amplified first before it is used for some useful purpose.
Applications of Photoelectric Cell:
Photoelectric cells are used in TV camera for telecasting scenes.
These cells are used for the reproduction of sound along with pictures in cinema.
Photocells are used in counting devices.
These cells are also used in burglar alarm and in fire alarm.
These cells are also used to measure the temperature of stars.
These cells are also used to switch on and off the street lighting system automatically.
These are used in photometry to compare the illuminating power of two sources.
These are used in industries to locate minor flows or holes in metallic sheets.
These are used as photoelectric sorters i.e. to sort out materials of different shades.
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