Unit of Specific Resistance Overview
The unit of specific resistance, also known as resistivity, is an essential concept in electrical engineering and physics. It refers to the inherent resistance of a material to the flow of electric current. This article will provide a detailed overview of the unit of specific resistance, including its definition, formula, units, and examples.
Unit of Specific Resistance: Definition
Specific resistance, denoted by the Greek letter ρ (rho), is a measure of the resistance of a material to the flow of electric current. It is defined as the resistance of a wire with a unit length and a unit cross-sectional area. In other words, specific resistance is the resistance per unit length and unit cross-sectional area of a material.
The specific resistance of a material is dependent on several factors, including the material's composition, temperature, and impurities. The resistivity of a material is usually expressed in units of ohm-meters (Ωm).
Unit of Specific Resistance: Formula
The formula for specific resistance is given as:
ρ = RA/L
Where:
ρ: Specific resistance (Ωm)
R: Resistance of the wire (Ω)
A: Cross-sectional area of the wire (m²)
L: Length of the wire (m)
From the formula, we can see that specific resistance is directly proportional to the resistance of the wire and the length of the wire. It is inversely proportional to the cross-sectional area of the wire.
Unit of Specific Resistance
From the specific Resistance Formula:
Unit of ρ=Unit of R×Unit of A / Unit of L
- Resistivity is obtained by expressing resistance R in Ohms (Ω) and distances in centimeters (cm).
- The SI unit of resistivity is Ohm cm (Ω .cm) when expressed in centimeters.
- If distances are expressed in meters (m), the SI unit of specific resistance becomes Ohm meter (Ωm).
- Conductivity is expressed in siemens.m-1 (S.m-1) or Ohm-1m-1.
- Metals have low specific resistance (∼10−8Ω.m) since they are good conductors, while insulators have high resistance (∼1016Ω.m) since they are poor conductors of electricity.
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Read More About: SI Unit of Resistance
Electrical Resistivity
Electric resistivity, which is also referred to as specific electrical resistance, is a characteristic of a material that indicates its ability to impede the flow of electric current. The symbol used to represent it is ρ, and its unit of measurement is ohm-meter in the International System of Units (SI).
Airway Resistance
The resistance encountered by air flowing through the respiratory tract during inhalation and exhalation is known as "airway resistance." This can be expressed using a formula analogous to Ohm's law:
RAW = ΔP/V
Where,
- ΔP= PATM-PA
- RAW = (PATM-PA)/V
- where RAW: airway resistance
- ΔP: pressure difference driving airflow
- PATM: atmospheric pressure
- PA: alveolar pressure
- V: volumetric airflow
Also Read About: Ohm's Law & Limitation of Ohm's Law
Unit of Specific Resistance of Copper
Copper has a specific resistance of 1.68 x 10-8Ω.m (20oC). This means that at a temperature of 20oC, the resistance between two opposite surfaces of a copper cube of side 1 m is 1.68 x 10-8 Ω.
- Copper has a conductivity of 5.96 x 107 Sm-1.
- Owing to its high conductivity and low resistivity, the resistance of copper to the flow of current is negligible.
- Copper wires are usually used to conduct electricity in electrical circuits.
Unit of Specific Resistance: Conversion Factor
The table below shows the conversion factors between different units of specific resistance.
|
Unit |
Conversion Factor |
|
1 Ωm |
100 Ωcm |
|
1 Ωm |
39.37 Ωin |
|
1 Ωcm |
0.01 Ωm |
|
1 Ωcm |
0.3937 Ωin |
|
1 Ωin |
0.0254 Ωm |
|
1 Ωin |
2.54 Ωcm |
Read More About: Dimension of Resistance
Unit of Specific Resistance of Other Materials
The specific resistance of various other materials are as follows –
|
Material |
Resistivity in Ohm meter (Ωm) |
|
Silver |
1.59 x 10-8 |
|
Copper |
1.68 x 10-8 |
|
Iron |
9.70 x 10-8 |
|
Gold |
2.44 x 10-8 |
|
Platinum |
1.06 x 10-7 |
|
Zinc |
5.90 x 10-8 |
|
Tin |
1.09 x 10-8 |
Unit of Specific Resistance: Things to Remember
- Resistivity refers to the amount of resistance a material offers per unit length and per unit cross-sectional area.
- The mathematical expression of resistance is given by ρ = RA/L.
- The SI unit of specific resistance is ohm-meter (Ωm).
- Superconductors exhibit zero resistivity in their superconducting state, which occurs at extremely low temperatures.
- Airway resistance is the resistance of the respiratory tract to the flow of air during inhalation and exhalation.
- Copper has a specific resistance of 1.68 x 10-8 Ω.m.
- Electrical resistivity is a measure of how effectively a material can impede the flow of electric current.