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Wednesday, 8 January 2020

Resistivity Of Electrical Material: Factors Effecting- Temperature, Alloying, Mechanical Stressing,Age Handling, Cold Working


Resistivity of Electrical Materials

  • Resistivity is the resistance per unit length and cross sectional area. It is the property of the material that opposes the flow of charge or the flow of electric current. 
  • The unit of resistivity is ohm meter.

Resistivity Of Varies matreials
Resistivity Of Varies matreials


Factors effecting the resistivity of electrical materials

1.      Temperature.

2.      Alloying.

3.      Mechanical stressing.

4.      Age Hardening.

5.      Cold Working.


Temperature 

  • The resistivity of materials changes with temperature. 
  • In some cases resistivity of most of the metals increase with temperature.  
  • The resistivity of metals increase with increase of temperature. It means the metals are having positive temperature coefficient of resistance. 
  • Several metals exhibit the zero resistivity at temperature near to absolute zero. This phenomenon is “called the superconductivity”. 
  • The resistivity of semiconductors and insulators decrease with increase in temperature. Means the semiconductors and insulators are having negative temperature coefficient of resistance.


Alloying

  • Alloying is a solid solution of two or more than two metals. Alloying of metals is useful to achieve some mechanical and electrical properties. 
  • The atomic structure of a solid solution is irregular as compared to pure metals. Due to which the electrical resistivity of the solid solution increases more rapidly with increase of alloy content. 
  • The impurity of silver (having lowest resistivity among all metals) in copper increase the resistivity of copper.


Mechanical Stressing 

  • The mechanical stressing of the crystal structure of material develops the localized strains in the material crystal structure. These localized stains disturb the movement of free electrons through the material. Because of this  increase in resistivity of the material.
  • Subsequently annealing of metal reduces the resistivity of metal. Annealing of metal, relieve the mechanical stressing of material due to which the localized stains got removed from the crystal structure of the metal.  Due to which the resistivity of metal decrease. 
  • For example, the resistivity of hard drawn copper is more as compared to annealed copper.


Age Hardening 

  • To develop the ability in alloys to resist its permanent deformation by external forces and  to increase age the yield strength hardening is a heat treatment process used.
  • Age hardening is also called “Precipitation Hardening”. 
  • Because of this process increases the strength of alloys by creating solid impurities or precipitate. 
  • These created solid impurities or precipitate, disturb the crystal structure of metal which interrupts the flow of free electrons through metal. Due to which the resistivity of metal increases.


Cold Working 

  • This is a manufacturing process used to increase the strength of metals. 
  • It is also known as “Work hardening” or “Strain hardening”. 
  • This cold working is used to increase the mechanical strength of the metal. 
  • Cold working disturbs the crystal structure of metals which interferewith the movement of electrons in metal, due to which the resistivity of metal increases.


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