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  • Fundamentals
    • What is a resistor?
    • Ohm’s law
    • Kirchhoff law
    • Electrical resistivity
    • Inductance
    • Capacitance
    • Resistance
    • Resistor properties
      • Noise
      • Temperature Coefficient
      • Power rating
  • Standards and codes
    • Color code
      • Color code calculator
    • Standard values
    • SMD codes
    • Resistor Sizes and Packages
    • Symbols
  • Types
    • Fixed
    • Variable
      • Potentiometer
        • Potentiometer taper
      • Digital potentiometer
      • Rheostat
      • Trimpot
    • Thermistor
      • NTC thermistor
      • PTC thermistor
    • Varistor
    • Magneto resistor
    • Photoresistor
  • Materials
    • Wirewound
    • Carbon composition
    • Carbon film
    • Metal film
    • Metal oxide film
    • Thin and thick film
  • Applications
    • In Parallel
      • Parallel resistor calculator
    • In Series
    • Heating
    • LED Current Limiting
    • Power
    • Pull up / Pull down
    • Automotive Blower
    • Shunt
    • Braking resistor
  • Resources
    • Books
    • Suppliers
  • Capacitor
Tag:

electrical conductivity temperature

  • Electrical resistivity

    by jwpustjens October 30, 2012
    by jwpustjens October 30, 2012
    What is electrical resistivity? Electrical resistivity is a measure of a material’s property to oppose the flow of electric current. This is expressed in Ohm-meters (Ω⋅m). The symbol of resistivity is usually the Greek letter ρ (rho). A high resistivity means that a material does not conduct well electric charge. Electrical resistivity is defined as the relation between the electrical field inside a material, and the electric current through it as a consequence: in which ρ is the resistivity of the material (Ωm), E is the magnitude of the electrical field in the material (V/m), J is the magnitude of the electric current density in the material (A/m2) If the electrical field (E) through a material is very large and the flow of current (J) very small, it means that the material has a high resistivity. Electrical conductivity is the inversion of resistivity, and is a measure of how well a material conducts electric current: in which σ is the conductivity of the material expressed in Siemens per meter (S/m). In electrical engineering often κ (kappa) is used instead of σ. Electrical Resistance Electrical resistance is expressed in Ohms, and is not the same as resistivity. While resistivity is a material property, resistance is the property of an object. The electrical resistance of a resistor is determined by the combination of the shape and the resistivity of the material. For example, a wirewound resistor with a long, thick wire has a higher resistance then with a shorter and thinner wire. A wirewound resistor made from a material with high resistivity has a higher resistance value then one with a low resistivity. An analogy with a hydraulic system can be made, where water is pumped through a pipe. The longer and thinner the pipe, the higher the resistance will be. A...
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