Electrical Conductivity/Resistivity

Definition

Electrical Resistivity is a measure of how a given material opposes current flow. Low resistivity shows a material that allows the flow of current, whereas the opposite is true for high resistivity. Electrical Conductivity is the reciprocal/inverse of Electrical Resistivity, in that it measures the ability of a given material to conduct electric current

Symbols

Electrical Resistivity is mainly represented by the Greek lower-case rho. Electrical Conductivity is mainly represented by the Greek lower-case sigma, but is occasionally represented by a lower-case kappa, or gamma.

SI Units

Electrical Resistivity is measured in Ohm-Metres. Electrical Conductivity is measured in Siemens per Metre

Classification of Materials by Conductivity

Materials with high Conductivity are known as conductors. ex. metals Materials with low Conductivity are known as resistors. ex. vacuums, glass, etc.

Semiconductors

Semiconductors are materials that have a conductivity in-between that of an insulator and a conductor. However, as temperature increases, unlike in most metals, the conductivity of semiconductors increases.

Temperature Dependence

As temperature increases, the electrical resistivity of metals increases. This is a reason why when computers heat up, they tend to slow down. Some materials exhibit superconductivity at extremely low temperatures. Below a certain temperature, resistivity vanishes, such as Pb at 7.20 K.

Equations

Poulliet's Law

R=ρℓ/A

          R = Electric Resistance
          ρ = Electric Resistivity
          ℓ = Length
          A = Cross-Sectional Area

Poulliet's Law states that a given materials resistance will increase in length, while it will decrease with an increase in Area.

Conductivity in Real Life

Conductors are used to carry electricity, as well as electrical signals in circuits. Complementary metal–oxide–semiconductors, or CMOS for short, are the foundational building block of gate based logic circuits, that make up the majority of all modern electronics. CMOS circuits are composed of a combination of p-type and n-type semiconductors. These semiconductors will change their conductivity, based on the applied voltage, allowing for logic of 0's and 1's, or low voltage and high voltage, to be transferred through logical circuits. This allows us to apply boolean logic to circuits, such as AND and OR logic, or even create an amalgamation of AND's and OR's to create electronics, such as multiplexors, switches, latches, registers, decoders, encoders, etc.

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External links

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