Conductivity

Claimed by myoung65, Spring 2016

Claimed by Reed Williams Fall 2016

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

Maxwell's Equation for Electric Conductivity'

J=(conductivity)E

          J= Electric Current Density
          E= Electric Field

Electric current density can be thought of as the electric current per cross sectional area of a specific material. Therefore this formula relates to each material differently. Every material has a specific conductivity associated with it, and this conductivity can help describe the electric field in each material. For example, materials such as copper and silver have extremely high electric conductivity and therefore in order to not have an almost infinite electric current density we can approximate the electric field inside the metals to be zero. This equation is essentially the proof for all metals having a zero electric field on the inside.

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.

https://www.youtube.com/watch?v=ODbgKXFED5o

History(New)

Stephen Gray, Father of Conduction

Born 1666 in Canterbury, England. Died 1736 in London, England.

Gray was an innovative thinker who performed many a experiment including work with the transmission of electricity. One day while performing one of his experiments, unbeknownst to him he discovered the difference between insulators and conductors. He was working with transmitting electricity and he changed the transmission wire from silk to brass wire when he noticed that electricity passes completely different in brass than it does in silk. After said discovery, Gray spend the next 3 years with the help of friends and family doing more research in similar topics, and with this research some might say solidified his name as the father of conduction.

See also

Are there related topics or categories in this wiki resource for the curious reader to explore? How does this topic fit into that context?

Further reading

Books, Articles or other print media on this topic

External links

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References

This section contains the the references you used while writing this page. Reeds Page

History: "Gray, Stephen." Complete Dictionary of Scientific Biography. . Encyclopedia.com. 25 Nov. 2016 <http://www.encyclopedia.com>.--Rwilliams354 (talk) 14:13, 27 November 2016 (EST)

Equations: "Conductivity." Maxwells-Equations.com, 2012. http://maxwells-equations.com/materials/conductivity.php --Rwilliams354 (talk) 14:10, 27 November 2016 (EST)