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In the previous article we learned as to how voltage is generated from heat, pressure and friction. In this article we will find out how voltage is produced from light.
Some substances have a tendency of generating potential when light strikes on their surfaces. As the light strikes the surface, electrons dislodges from the orbits of the atoms of the substance. Many substances are highly sensitive to light. This means that higher the intensity of light striking the surface, higher amount of electrons will be dislodged from the orbits. These highly sensitive metals are known as photo-sensitive metals. Also, as more and more electrons are released from the atoms’ orbits, an electric force is generated. This voltage generated can be used as a power source and is termed as photoelectric voltage.
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Generally most of the metals are light sensitive, however there are few which are far more sensitive than others. Various compounds of silver or copper oxide are the most commonly used photo-voltaic materials used to generate photo-electric voltage. All the materials that use this phenomenon to generate electricity are known as photo voltaic cells.
Photo voltaic cells are abundantly used in today’s world. Different types and sizes of photovoltaic cells are available in the market, having their own special purpose. However, all use the same concept.
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Generating Voltage From Light
In figure A, an anode (one with electrons) is placed at the center of a curved light sensitive surface which is angled towards the anode. A light source is placed exactly in front of the surface. When the light strikes the surface, electrons are emitted from the orbits of the atoms of the substance. These electrons get deposited on the anode. A wire connects the anode and the back (black) side of the photosensitive surface. The electrons released from the anode get transferred to the back of the material surface through this wire. These electrons take the place of those released when light strikes the material surface. In this way a continuous flow of electrons takes place and this current can be used for some useful purpose.
Mostly all the cells are constructed in layers with a base plate consisting of pure copper and a layer of photosensitive copper oxide over it. In some cases an extremely thin semi- transparent layer of metal is placed over the copper oxide. This layer serves two purposes – it allows penetration of light to the copper oxide and collects the electrons emitted by copper oxide.
However, the magnitude of voltage generated is very low which makes it less practical. Photo-sensitive surface have a characteristic of light intensity variation in a very short time. It is this property that makes it useful in many applications. Some applications of photo voltaic cells are burglar alarms, door openers, television cameras etc.
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