When the dielectric material is placed in an electric field, the electric field realigns the dipoles resulting in polarization. Polarization occurs in a dielectric material when it is subjected to an external electric field. There are four polarisation mechanisms. They are Electronic polarization, Ionic polarization, Orientation polarisation and Space charge polarisation. Electronic or Induced Polarisation
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Depending on the separation between the centre of gravity of positive charges and the centre of gravity of negative charges, the dielectrics are classified as polar (dipole) dielectrics and non-polar (neutral) dielectrics. Polar molecules The polar molecule is one in which it will not have centre of symmetry. Here the ‘centres’ of positive and negative
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The dielectric materials may be classified as solid, liquid and gas dielectrics. Solid form In solid form they may be polymeric such as nylon, pvc, rubber, backlite, asbestos and wool or may belong to the ceramic family such as glass, silica, mica, porcelain, etc. Liquid form form In liquid form they may be mineral insulating
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Engineering applications Based on their properties, they have the following applications. Since there is no loss in power (zero resistivity) super conductors can be used for the transmission of power over very large distance. Since, the super conducting property can be easily destroyed it can be used in switching devices. It can be used in
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Based on the value of superconducting transition temperature, superconductors are divided into two categories: (i) Low temperature superconductors (ii) High temperature superconductors S.No Low Temperature superconductor High Temperature superconductor 1. Superconductors having low superconducting transition temperature (<20 K). Superconductors having high superconducting transition (>100 K). 2. Due to the formation of superconductivity from holes, it
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Impurities : When the impurities are added to superconducting material, the properties can be changed abruptly. In particular the magnetic properties can be changed. Size : If the size is reduced below 100μm the superconducting properties such as magnetic permeability is no longer zero and critical magnetic field (Hc) increases than bulk material. Frequency :
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In 1911, Kammerlingh onnes while studying the electrical behaviour of metals at low temperatures, he observed that the resistivity of impure metals decreased with temperature and had a finite valve at 0K. But for mercury the resistivity decreased gradually as the temperature is reduced, but abruptly dropped to zero at 4.2K (Figure). Below this temperature,
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On the basis of size of heterocyclic rings, classification of these compounds is done into following types: Five-Membered Heterocyclic Compounds: These are five membered ring compounds consisting of one hetero atom and four carbon atom. Six-Membered Heterocyclic Compounds: These compounds contain six atom ring in which five atoms are carbon while one is hetero atom.
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Conformational isomers or rotamers are infinite numbers of momentary arrangements of groups or atoms in space that results due to the rotation about a single bond. Factors affecting conformational stability of a molecule are: Steric Strain: Steric strain or Van der Waal’s strain is developed when distance between two non-bonded atoms is less than the
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In stereospecific reactions, one stereoisomer of the product is obtained if one stereoisomer of the reactant is present, while different stereoisomers of product are obtained when different stereoisomer of the reactant are present. Thus for determining whether a reaction is stereospecific or not, one has to analyse the product ratio from the different stereoisomer of
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