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.
resistivity :
The electrical resistance per unit length, area, or volume of a substance is known as resistivity.
Table of resistivity
| Material | Resistivity ρ (ohm m) | Temperature coefficient α per degree C | Conductivity σ x 107 /Ωm | Ref | |
| Silver | 1.59 | x10-8 | .0038 | 6.29 | 3 |
| Copper | 1.68 | x10-8 | .00386 | 5.95 | 3 |
| Copper, annealed | 1.72 | x10-8 | .00393 | 5.81 | 2 |
| Aluminum | 2.65 | x10-8 | .00429 | 3.77 | 1 |
| Tungsten | 5.6 | x10-8 | .0045 | 1.79 | 1 |
| Iron | 9.71 | x10-8 | .00651 | 1.03 | 1 |
| Platinum | 10.6 | x10-8 | .003927 | 0.943 | 1 |
| Manganin | 48.2 | x10-8 | .000002 | 0.207 | 1 |
| Lead | 22 | x10-8 | ... | 0.45 | 1 |
| Mercury | 98 | x10-8 | .0009 | 0.10 | 1 |
| Nichrome (Ni,Fe,Cr alloy) | 100 | x10-8 | .0004 | 0.10 | 1 |
| Constantan | 49 | x10-8 | ... | 0.20 | 1 |
| Carbon* (graphite) | 3-60 | x10-5 | -.0005 | ... | 1 |
| Germanium* | 1-500 | x10-3 | -.05 | ... | 1 |
| Silicon* | 0.1-60 | ... | -.07 | ... | 1 |
| Glass | 1-10000 | x109 | ... | ... | 1 |
| Quartz (fused) | 7.5 | x1017 | ... | ... | 1 |
| Hard rubber | 1-100 | x1013 | ... | ... | 1 |
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[…] 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 […]
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