Short Answer
Conductivity is the property of a material that tells how easily electric current can flow through it. A material with high conductivity allows electric charges to move freely, while a material with low conductivity does not allow charges to flow easily. Metals like copper and silver have very high conductivity, whereas rubber and plastic have extremely low conductivity.
Conductivity is the opposite of resistivity. It is measured in siemens per metre (S/m). Conductivity helps us understand which materials are good conductors and which are poor conductors in electrical circuits and devices.
Detailed Explanation
Conductivity
Conductivity is an important physical property that describes how well a material can conduct electric current. It tells us how easily electrons or charged particles can move through the material when a potential difference is applied. Materials that allow charges to flow easily are called good conductors, while those that do not allow charges to flow are called insulators.
Conductivity plays a major role in deciding which materials should be used in wires, electronic devices, heating elements, insulators, and many other applications. Understanding conductivity helps us compare different materials based on their ability to carry electric current.
Meaning of conductivity
Conductivity refers to the ability of a material to let electric current pass through it. When a voltage is applied across a material, free electrons (in metals) or ions (in liquids) begin to move. If the material has many free electrons or ions, the current flows easily and the conductivity is high. If the material has very few charge carriers, the current flows poorly and the conductivity is low.
Thus, conductivity depends mainly on:
- Number of free electrons or charge carriers
- Temperature of the material
- Structure and type of material
Relation between conductivity and resistivity
Conductivity is the inverse of resistivity.
The formula is:
σ = 1 / ρ
Where,
- σ (sigma) = conductivity
- ρ (rho) = resistivity
This means:
- If a material has high resistivity, its conductivity is low.
- If resistivity is low, conductivity is high.
For example:
- Copper has low resistivity → high conductivity.
- Rubber has high resistivity → extremely low conductivity.
This relationship helps classify materials easily.
Unit of conductivity
The SI unit of conductivity is siemens per metre (S/m).
Older units include mho/m (ohm spelled backward), but S/m is now standard.
Types of materials based on conductivity
- Conductors
- High conductivity
- Many free electrons
- Examples: Copper, silver, gold, aluminum
These are used in wires, cables, and electrical machines.
- Insulators
- Very low conductivity
- Very few free electrons
- Examples: Rubber, plastic, glass
These are used to cover wires and prevent electric shock.
- Semiconductors
- Moderate conductivity
- Conductivity increases with temperature
- Examples: Silicon, germanium
These are used in electronic devices like diodes and transistors.
- Electrolytes
- Conductivity due to ions
- Examples: Saltwater, acids, bases
Factors affecting conductivity
- Material type:
Metals with many free electrons have high conductivity.
Insulators with tightly bound electrons have low conductivity. - Temperature:
- In metals: Conductivity decreases with temperature because atoms vibrate more and obstruct electron flow.
- In semiconductors: Conductivity increases with temperature because more electrons become free.
- Impurities:
Adding impurities can change conductivity.
For example, adding impurities to silicon greatly increases its conductivity (doping). - State of matter:
- Solids: Conduct through electrons.
- Liquids: Conduct through ions.
- Gases: Conduct only when ionized.
Why conductivity is important
Conductivity helps us choose the right material for the right purpose:
- For wiring:
High-conductivity materials like copper and aluminum are used. - For insulation:
Low-conductivity materials like plastic and rubber are used. - For electronics:
Semiconductors with controlled conductivity are used. - For batteries and electrolysis:
Liquid electrolytes with ionic conductivity are essential. - For sensors and heaters:
Materials with specific conductivity values are needed.
Conductivity also helps in understanding heat conduction because good electrical conductors are often good thermal conductors too.
Examples of conductivity in daily life
- Copper wires:
Used in houses because copper has high conductivity. - Plastic coatings on wires:
Used as insulation because plastic has very low conductivity. - Saltwater:
Conducts electricity due to the presence of ions. - Microchips:
Use silicon with controlled conductivity. - Lightning:
Air gains conductivity when ionized, allowing current to pass.
These examples show how conductivity affects our daily life.
Conclusion
Conductivity is the property of a material that indicates how easily electric current can flow through it. It is the opposite of resistivity and is measured in siemens per metre. Materials with high conductivity, like metals, allow current to flow easily, while insulators restrict current. Conductivity is essential in choosing materials for wiring, insulation, electronics, and many other electrical applications.