Conductor,Semiconductor and Insulator Notes For ECE of SSC Scientific Assistant Exam 2017

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Conductors are generally substances which have the property to pass different types of energy. In the following, the conductivity of electricity is the value of interest.

Metals: The conductivity of metals is based on the free electrons (so-called Fermi gas) due to the metal bonding. Already with low energy electrons become sufficiently detached from the atoms and a conductivity is achieved.

The conductivity depends, inter alia, on the temperature. If the temperature rises, the metal atoms swing ever stronger, so that the electrons are constrained in their movements. Consequence, the resistance increases. The best conductors, gold and silver, are used relatively rare because of the high costs (gold e.g. for the contacting of the finished chips). The alternatives in the semiconductor technology for the wiring of the individual components of microchips are aluminum and copper.

Salts: In addition to metals, salts can also conduct electricity. There are no free electrons, so the conductivity depends on ions which can be solved when a salt is melting or dissolving, so that the ions are free to move

Insulators: Glass, most polymers (plastics), rubber and wood are all examples of insulators. These are materials which will refuse to carry an electric current. They are useful for jobs like coating electric wires to prevent them from ‘shorting together’ or giving you a shock. Silk and cotton are also good insulators (when they’re dry!!) and some of the mains wiring in very old houses once used them – but by modern standards this was pretty dangerous since you could get a shock when wet or a spark would set them alight when dry. Modern insulators like PVC (PolyVinylChloride) are much better and safer.Insulators are also very useful to fill the ‘gap’ in between the metal plates of a capacitor.

Semiconductors are solids whose conductivity lies between the conductivity of conductors and insulators. Due to exchange of electrons – to achieve the noble gas configuration – semiconductors arrange as lattice structure. Unlike metals, the conductivity increases with increasing temperature. Increasing temperatures leads to broken bonds and free electrons are generated. At the location at which the electron was placed, a so-called defect electron (“hole”) remains.

 

Image result for resistivity value between conductor semiconductor and insulator

 

  • PRAGATI GUPTA

    Dear Sir, in ssc assistant scientist i filled bachelor equivalent because i complete my B.tech in ECE. and there is only diploma option for ECE. then what comes in my paper 2 exam, sir, please guide me.