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resistance & resistivity

Resistance is a measure of the opposition to current flow in an electrical circuit.


Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Ohms are named after George Simon Ohm (1784-1854), a German physicist who studied the relationship between voltage, current and resistance. He is credited for formulating Ohm’s Law.

The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it.

The higher the resistance, the lower the current flow and vice-versa.



ohms-law-cartoon-cropped

resistivity :


The electrical resistance per unit length, area, or volume of a substance is known as resistivity.


Table of resistivity




























































































































































MaterialResistivity ρ
(ohm m)		Temperature
coefficient α
per degree C		Conductivity σ
x 107 /Ωm		Ref
Silver1.59x10-8.00386.293
Copper1.68x10-8.003865.953
Copper, annealed1.72x10-8.003935.812
Aluminum2.65x10-8.004293.771
Tungsten5.6x10-8.00451.791
Iron9.71x10-8.006511.031
Platinum10.6x10-8.0039270.9431
Manganin48.2x10-8.0000020.2071
Lead22x10-8...0.451
Mercury98x10-8.00090.101
Nichrome
(Ni,Fe,Cr alloy)		100x10-8.00040.101
Constantan49x10-8...0.201
Carbon*
(graphite)		3-60x10-5-.0005...1
Germanium*1-500x10-3-.05...1
Silicon*0.1-60...-.07...1
Glass1-10000x109......1
Quartz
(fused)		7.5x1017......1
Hard rubber1-100x1013......1

learn about resistor and resistor color codes 
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Comments

  1. Kirchhoff laws | THE JARGONMay 14, 2017 at 2:34 AM

    […] Kirchhoff Current and Voltage laws. These laws are very helpful in determining the equivalent electrical resistance or impedance (in case of AC) of a complex network and the currents flowing in the various branches […]

    ReplyDelete
  2. THE JARGONJune 10, 2017 at 3:52 AM

    […] →1.3 Resistance & Resistivity […]

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