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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