Optronic Devices and Their Uses

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Optronic Devices and their uses Optronic devices can be classified into two groups. 1. Photovoltaic devices 2. Photoconductive devices Photoconductive devices such as photo resistors are widely used in counting systems, twilight switches, house security systems etc. These detect variations in the light intensities and activate or deactivate electronic circuits. Photodiodes and phototransistors also fall in this category. These utilize the reverse biased junctions for generating current when illuminated. Photovoltaic devices produce a voltage when these are exposed to light. The light energy produces a potential difference across the p-n junction depending on the intensity of the incident light. Solar cells and photovoltaic cells are widely used in various applications to generate electricity. Photovoltaic cells: A photo-voltaic cell consists of many p-n junctions connected in series. One of the junctions is very thin, so light can easily pass through it. When light passes, charge carriers such as holes and electrons are produced proportional to the incident light. Uses: Photovoltaic cells are used in various applications to generate electricity where mains power is not available. Examples include solar cells and solar batteries, which are used in satellites. Photoconductive cells: Photoconductive cells use a semiconductor material whose electrical conductivity varies with the intensity of the incident light. Light-dependent resistors (LDRs) are typical photoconductive cells. When light falls on the semiconductor material, its conductivity increases. Normally, cadmium sulphide (CdS) is used in LDRs and their resistance depends on the intensity of light. CdS cells have a sensitive area that contains small amounts of silver, antimony, or indium impurities. The electron-hole pairs produced by the incident light increase

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