General properties of matter

Elasticity : All most all the substances can be more or less be deformed by applying suitable deforming forces. Some of the substance regain their original shape and size on the removal of deforming force. The property of the substance due to which it regain its original shape and size on the removal of deforming forces is known as elasticity. The substance which completely regain its original shape and size on the removal of deforming forces are known as perfectly elastic but the substance which completely retain its changed dimensions are known as perfectly plastic.Stress : Whenever a deforming force is applied to bring a change in the...

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FORWARD BAIS & REVERSE BAIS

If a battery is connected across a P - N junction with its positive terminal joined to the N - type side and its negative terminal to the p type side, it helps the junction voltage and the junction is said to be REVERSED BAISED. Electrons and holes are repelled further from the junction and the depletion layer winds only a few thermally generated minority carrier cross the junction and a very small current, called reverse current or leakage flows. If a battery is connected across a P - N junction with its positive terminal joined to the P...

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P - N JUNCTION

When a P -type material is placed in contact with an N - type material the contact surface is called P - N junction. As soon as the junction is produced free electrons near the junction in the N - type material move across the junction in the P - type material , where they fill the holes as the result a positive charge is appears near the junction in the N - type material and the negative charge appears in the near the P - type material. At the same time holes diffuse across the junction from the P -type to the N - type material. The exchange of the charge soon stops because the positive charge on the on the N - type side opposes...

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Formation of P - type semiconductor

A P - type semiconductor is formed when a small amount of trivalent impurity is added to pure Germenium or silicon atom crystal. The addition of trivalent impurity produces a large no. of holes to the host crystals. To explain the formation of P - type semiconductor, let us introduce a trivalent impurity into the lattice of a pure silicon crystal. The trivalent atom has 3 valance electrons and form covalent bonds with neighbouring atoms. The 4th bond is incomplete . the trivalent atom then attracts an electron from an adjacent atom there by completing the 4th bond and forming a hole in the adjacent atom. Since a trivalent impurity atom provides...

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Formation of N - type semiconductor

An N - type semiconductor is formed when a small amount of pentavalent impurity is added to a pure Germenium or Silicon crystal. The addition of pentavalent impurity produces a large no. of free electrons in the host crystal.To explain the formation of N - type semiconductor, let us introduce a pentavalent impurity atom into the lattice of pure silicon crystal. The pentavalent atom has 5 valance electrons, but only 4 form covalent bonds with the neighbouring atoms. The 5th electron finds no place in the covalent bonding so becomes free. Since an impurity atom provides one free electron, an enormous increase occurs in the no. of free electrons....

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Semiconductors contd.......

For metals, the valance and conduction bands can overlap. The electrons in the overlapping region of energy are conduction electrons. Since there is large number of conduction electrons, the metals are good conductors.An intrinsic semiconductor is a pure semiconductor. for instance, a silicon crystal is an intrinsic semiconductor if energy energy atom in the crystal is silicon atom.A pure semiconductor has a very small electrical conductivity at ordinary temperature however, its conductivity can be increased appreciably by adding a small amount of trivalent impurity or pentavalent impurity to it. The process of adding the impurity is called...

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Semiconductors

A semiconductor is a material whose conductivity lies between that of good conductor & good insulator . Silicon and germanium are the examples of semiconductors widely used in the electronics industry .According to the band theory, semiconductors are a class of material in a narrow forbidden band. The energy gap is the order of 1 eV . At absolute zero, the valance band energy levels are completely filled by by electrons, the conduction band is empty, & the material is then an insulator. At normal temperature, the thermal energy of some electrons is sufficient for them to reach the conduction band, where they become conduction electrons....

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