Electrical Conductivity
Understanding electrical conductivity and its properties.
What is Electrical Conductivity?
Electrical conductivity (symbol: σ, sigma) is a measure of a material's ability to conduct electric current. It is the reciprocal of electrical resistivity. High conductivity indicates a material that readily allows the flow of electric charge.
Units of Conductivity
| Unit | Symbol | Description |
|---|---|---|
| Siemens per meter | S/m | The SI unit of electrical conductivity. |
| Mho per meter | ℧/m | An older, equivalent unit (mho is ohm spelled backward). |
Relationship with Resistivity
σ = 1 / ρ
Where:
• σ = Conductivity (Siemens per meter, S/m)
• ρ = Resistivity (Ohm-meter, Ω·m)
Where:
• σ = Conductivity (Siemens per meter, S/m)
• ρ = Resistivity (Ohm-meter, Ω·m)
Factors Affecting Conductivity
- Material: Different materials have different inherent conductivities. Metals are generally good conductors, while non-metals are often insulators.
- Temperature: For most metals, conductivity decreases with increasing temperature due to increased atomic vibrations hindering electron flow. For semiconductors, conductivity can increase with temperature.
- Impurities: The presence of impurities can significantly affect a material's conductivity.
Common Conductivity Values
| Material | Conductivity (S/m at 20°C) | Classification |
|---|---|---|
| Silver | 6.30 × 107 | Conductor (Highest) |
| Copper | 5.96 × 107 | Conductor |
| Gold | 4.52 × 107 | Conductor |
| Aluminum | 3.77 × 107 | Conductor |
| Seawater | 5 | Conductor (Weak) |
| Pure Water | 5.5 × 10-6 | Insulator (Very Weak Conductor) |
| Glass | 10-10 to 10-14 | Insulator |
| Rubber | 10-13 to 10-16 | Insulator |
Frequently Asked Questions
What is the difference between conductivity and conductance?
Conductivity is an intrinsic material property (how well a material conducts electricity), while conductance is a property of a specific object made of that material, depending on its shape and size.
Why are some materials better conductors than others?
Materials with many free electrons (like metals) are good conductors because these electrons can move easily throughout the material, carrying electric charge. Insulators have very few free electrons.