What is Specific Resistance : Formula and Its Units

The resistivity otherwise specific resistance is the resistance in ohms recommend through a material that has a unit volume to the current supply. Resistivity is the mutual of conductivity. A material that has resistivity high, then the conductivity will below. Therefore, an exact resistance of a material is the resistance of a unit volume of that substance. There are many materials available that depend on the resistance in ohms of a material volume This article discusses an overview of this resistance and its formula.

What is Specific Resistance?

Specific resistance is the resistance accessible for each unit length as well as unit cross-sectional area once the recognized quantity of voltage is applied. Mathematically specific resistance formula is represented like the following.


ρ = RA/L

Where,

‘⍴’ is a specific-resistance
‘R’ is the resistance
‘A’ is the cross-sectional area
‘L’ is the material’s length

The unit of specific resistance is ohm meter or Ωm

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resistivity or specific resistance
resistivity or specific resistance

This is common for specific conductance, and it can be defined as a calculation of the ability of a substance to conduct electrical energy. The specific conductance can be denoted with ‘k’. It can also refer to specific electric or airway resistance

Materials at 20oC

The resistance of different substances at 20oC is listed below.

  • For material Nichrome, the resistance is 675 ohm-circular mil/ft and 112.2 micro ohm-cm
  • For material Nichrome V, the resistance is 650 ohm-circular mil/ft and 108.1 micro ohm-cm
  • For material Manganin, the resistance is 290 ohm-circular mil/ft and 48.21 micro ohm-cm
  • For material Constantan, the resistance is 272.97 ohm-circular mil/ft and 45.38 micro ohm-cm
  • For material Steel, the resistance is 100 ohm-circular mil/ft and 16.62 micro ohm-circular
  • For material Platinum, the resistance is 63.16 ohm-circular mil/ft and 10.5 micro ohm-cm
  • For material Iron, the resistance is 57.81 ohm-circular mil/ft and 9.61 micro ohm-cm
  • For material Nickel, the resistance is 41.69 ohm-circular mil/ft and 6.93 micro ohm-cm
  • For material Zinc, the resistance is 35.49 ohm-circular mil/ft and 5.90 micro ohm-cm
  • For material Molybdenum, the resistance is 32.12 ohm-circular mil/ft and 5.34 micro ohm-cm
  • For material Tungsten, the resistance is 31.76 ohm-circular mil/ft and 5.28 micro ohm-cm
  • For material Aluminum, the resistance is 15.94 ohm-circular mil/ft and 2.650 micro ohm-cm
  • For material Gold, the resistance is 13.32 ohm-circular mil/ft and 2.214 micro ohm-cm
  • For material Copper, the resistance is 10.09 ohm-circular mil/ft and 1.678 micro ohm-cm
  • For material Silver, the resistance is 9.546 ohm-circular mil/ft and 1.587 micro ohm-cm

The specific electrical resistance can also be called electric resistivity and it is the property of a substance that defines a substance that opposes the flow of current very strongly.

What is Airway Resistance?

Airway resistance is the topic of respiratory physiology. It can be defined as the resistance of the respiratory region airflows through inhaling & exhaling. This formula is related to Ohm’s law which is shown below.

RAW=ΔP/V

Where,

ΔP = PATM−PA RAW = PATM−PAV˙

Where,

RAW is airway resistance
ΔP is pressure disparity driving airflow
PATM is the pressure of atmospheric
PA is the pressure of alveolar
V is the volumetric airflow

The specific resistance of copper is a good conductor at 1.72 x 10-8 ohm meter as well as the specific resistivity of air is a poor conductor at1.5 x 1014 ohm meter.

Thus, the specific resistance of a conductor is the unit length &  cross-section area of the conductor’s resistance. The property of a substance is when resistance is not available. Once the specific resistance of a conductor increases with long length then the resistance will be decreased through the cross-section area. Here is a question for you, what is the specific-resistance of copper?

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