10-11-2012, 11:42 AM
to study various factors on which internal resistance depends
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investigatory projects in physics for class 12
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to study various factors on which internal resistance depends
24-11-2017, 05:40 PM
Class 12 Investigatory project on SemiConductors
25-11-2017, 10:36 AM
A semiconductor material has a value of electrical conductivity that falls between that of a conductor, such as copper, and an insulator, such as glass. Its resistance decreases as its temperature increases, which is the opposite behavior to that of a metal. Their conductive properties can be altered in useful ways by the deliberate and controlled introduction of impurities ("doping") into the crystalline structure. Where there are two regions doped differently in the same crystal, a semiconductor junction is created. The behavior of charge carriers that include electrons, ions and electron holes in these junctions is the basis of diodes, transistors and all modern electronics.
Semiconductor devices can show a range of useful properties such as passing current more easily in one direction than the other, showing variable resistance and sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by doping, or by the application of electric or light fields, devices made from semiconductors can be used for amplification, switching, and energy conversion.
The modern understanding of the properties of a semiconductor is based on quantum physics to explain the movement of charge carriers in a crystal lattice. Doing greatly increases the amount of charge carriers inside the crystal. When a doped semiconductor contains mainly free holes it is called "p-type", and when it contains mostly free electrons it is known as "type n". The semiconductor materials used in electronic devices are doped in precise conditions to control the concentration and regions of the dopant type p and n. A single semiconductor crystal can have many regions of type p and n; the p-n junctions between these regions are responsible for the useful electronic behavior.
Although some pure elements and many compounds show semiconductor properties, silicon, germanium and gallium compounds are the most widely used in electronic devices. The elements near the so-called "metalloid staircase", where the metalloids are located in the periodic table, are generally used as semiconductors.
Some of the properties of semiconductor materials were observed during the middle of the 19th century and the first decades of the 20th century. The first practical application of semiconductors in electronics was the development in 1904 of the Cat's-whisker detector, a primitive semiconductor diode widely used in the first radio receivers. The developments in quantum physics in turn allowed the development of the transistor in 1947 and the integrated circuit in 1958.
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