# 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

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?