It is a parameter which indicates how easily electric current can flow through

It is a parameter which indicates how easily electric

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It is the property of a material to allow the flow of electric current. It is a parameter which indicates how easily electric current can flow through the material. It is denoted by ‘σ’. Conductivity of material is the reciprocal of resistivity. Conductivity of material can be determined by, Its SI unit is 1/(Ω -meter) or /meter. Dielectric Strength It is the property of material which indicates the ability of material to withstand high voltages. Generally it is specified for insulating material to represent their operating voltage. A material having high dielectric strength can withstand high voltages. Generally, it is represented in the unit of kV/cm. Dielectric strength of some insulating materials are listed below. S/No. Material Dielectric Strength [kV (max.)/cm] 1 Air 30 2 Porcelain 80 3 Paraffin Wax 120 4 Transformer oil 160 5 Bakelite 220 6 Rubber 280 7 Paper 500 8 Teflon 600 9 Glass 1200 10 Mica 2000 Temperature Coefficient of Resistance The temperature coefficient of resistance of a material indicates the change in resistance of material with change in temperature. Resistance of conductor changes with change of temperature. The rise in resistance of a material with rise in temperature depends on following things: 1. R 2 - R 1 R 1 2. R 2 - R 1 t 2 - t 1 3. Property of material of conductor. where, R 1 is the resistance of a conductor at temperature of t 1 °C, and
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~ Page 32 of 79 ~ R 2 is the resistance of a conductor at temperature of t 2 °C. Hence, from above, R 2 - R 1 R 1 (t 2 - t 1 ) Or, R 2 - R 1 = α 1 R 1 (t 2 - t 1 ) R 2 = R 1 [1+α 1 (t 2 - t 1 )] where, α 1 is temperature coefficient of resistance of material at temperature of t 1 °C. Its unit is /°C. Temperature coefficient of resistance of material also depends on temperature. Temperature coefficient of resistance of some materials are listed below, S/No. Element Temperature Coefficient of Resistance in /°C 1 Manganin 0.00002 2 Constantan 0.00017 3 Nichrome 0.0004 4 Mercury 0.0009 5 Silver 0.0038 6 Copper 0.00386 7 Annealed copper 0.000393 8 Platinum 0.003927 9 Aluminium 0.00429 10 Carbon ( Graphite) - 0.0005 11 Germanium - 0.05 12 Silicon - 0.07 Thermoelectricity If the junction, formed by joining two metals, is heated, a small voltage in the range of millivolt is produced. This effect is called thermoelectricity or thermoelectric effect. This effect forms the basis of operation of thermocouples and some temperature based transducers. This effect can be used to generate electricity, to measure the temperature and to measure the change in temperature of objects.
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~ Page 33 of 79 ~ Magnetic Properties of Engineering Materials To finalize the material for an engineering product / application, we should also have the knowledge of magnetic properties of materials . The magnetic properties of a material are those which determine the ability of material to be suitable for a particular magnetic application. Some of the typical magnetic properties of engineering materials are listed below: o Permeability o Retentivity or Magnetic Hysteresis o Coercive force o Reluctance Permeability It is the property of magnetic material which indicates how easily the magnetic flux builds up in the material.
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