... ohms), A is the material's cross-sectional area (in m2), and l is the material's length (in m). Conductivity: Conductivity (represented by the symbol ? and typically expressed in units of ohm-1*m-1) is a material's ability to transport energy from one location to another, and is defined to be the reciprocal of resistivity. It is directly proportional to how mobile the electrons or ions are in a material. Alternatively, conductivity can be expressed as the ratio of electrical charge flux to unit voltage gradient, which can be described mathematically by the following formula, where V is the voltage difference experienced across a given length of the material (in volts) and d is the distance over which the voltage difference occurs (in m). Insulator: An insulator (sometimes referred to as a dielectric) is a substance whose electrons are not free to move, and through which electric current only passes with difficulty or cannot pass ...

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