SI and CGS Units of Conductivity in Physics and Chemistry
Conductivity is a fundamental concept in Physics that measures how easily electric charge or heat can pass through a material. It plays a vital role in understanding materials as conductors or non-conductors in various practical and theoretical applications of Electricity and Magnetism.
A material with high conductivity allows electric current or heat to flow freely and is called a conductor. Metals are typical examples of such materials due to the presence of free electrons that enable the flow of charge. On the other hand, materials with very low conductivity are called non-conductors or insulators.
Electrical conductivity is also known as specific conductance. It is especially important in evaluating substances like metals, electrolytes, and non-metals to determine how efficient they are in transmitting electricity or heat. Understanding this property is crucial for solving Physics numerical problems and performing laboratory measurements.
Definition and Explanation of Conductivity
Conductivity quantifies the ease with which electric charge (or heat) flows through a material. The higher the conductivity, the better the material can allow current to pass. Electrical conductivity is a physical property found widely in Physics, Chemistry, and Engineering.
If a material opposes the flow of electricity, it is an insulator (non-conductor). If it allows smooth and easy flow, it is a conductor. For example, copper and aluminum are good conductors, whereas rubber and glass are insulators.
SI Unit of Conductivity
The SI unit of electrical conductivity is Siemens per metre, written as S/m. This unit expresses how much electric current passes through a material per unit electric field per metre length.
In earlier textbooks, the old unit "mho per metre" (mho/m) was used. The modern and accepted form is Siemens per metre (S/m).
| Physical Quantity | Unit Name | Symbol | Old Unit |
|---|---|---|---|
| Conductivity | Siemens per metre | S/m | mho/m |
Metals such as silver, copper, and aluminum have very high conductivity, making them ideal for electrical wiring and connections. Non-metals generally have much lower conductivity, and materials like plastic or glass are mainly used to insulate and prevent the flow of current.
Formula for Conductivity
The mathematical relationship connecting conductivity and resistance (or resistivity) is a key formula in Physics:
- Conductivity (σ) is the reciprocal of resistivity (ρ).
- Mathematically: σ = 1 / ρ
- Here, σ (Greek letter sigma) is conductivity, ρ (rho) is resistivity.
Differentiating Conductors and Non-Conductors
A material with high conductivity is called a conductor. These materials make efficient pathways for the movement of electrons. Most metals fall into this category.
If a material has very low conductivity, it is termed a non-conductor or insulator. Examples include wood, plastic, and glass.
| Type of Material | Conductivity | Example |
|---|---|---|
| Conductor | High | Copper, Silver |
| Non-conductor | Low | Plastic, Glass |
Example Problem: Finding Conductivity
Suppose you need to find the conductivity of a metallic wire. If its resistivity (ρ) is 2 × 10-8 Ω·m:
- Use the formula σ = 1 / ρ
- σ = 1 / (2 × 10-8) = 5 × 107 S/m
- So, the conductivity is 5 × 107 Siemens per metre.
Stepwise Approach for Problem Solving
| Step | What to Do |
|---|---|
| 1 | Identify what is given: resistance, resistivity or conductance. |
| 2 | Check the required physical quantity: conductance or conductivity. |
| 3 | Use the correct formula (for example, σ = 1 / ρ). |
| 4 | Ensure all units are in SI (Ω·m for resistivity, S/m for conductivity). |
| 5 | Calculate and write the answer with the correct unit. |
Key Points and Applications
- The SI unit of conductivity is Siemens per metre (S/m).
- Materials with high conductivity are vital for electrical circuits and devices.
- Non-conductors are used for insulation to prevent loss of current.
- Electrical conductivity is also known as specific conductance.
- This concept is essential for solving Physics numerical questions on electricity.
Further Learning and Practice
- To explore more, read about Conductivity.
- Learn about Conductors and Insulators in Physics.
- Dive deeper into the Conductivity of Water and its uses.
- Review Electrical Conductivity for applied Physics problems.
- Strengthen your fundamentals with Unit of Conductivity topic resources.
Mastering the concept of conductivity and its SI unit enables you to analyze materials efficiently and helps in scoring well in Physics. It is directly connected to practical applications, theoretical understanding, and problem-solving skills required in competitive exams and class assessments.
FAQs on Unit of Conductivity: Definition, SI Unit & Examples
1. What is the SI unit of conductivity?
The SI unit of conductivity is Siemens per metre (S/m). This unit is also written as S·m-1. Conductivity, commonly denoted by the Greek letter κ (kappa), measures how easily electric current flows through a material. (Source: NCERT Physics, CBSE 2025 syllabus)
2. What is the symbol of conductivity?
The standard symbol of conductivity is the Greek letter κ (kappa). Sometimes, the symbol σ (sigma) is also used, but κ is preferred in most Physics and Chemistry textbooks. This symbol is important for formulas and exam answers.
3. Is Siemens the same as mho for conductivity unit?
Yes, Siemens (S) and mho mean the same unit for conductance and conductivity. Siemens is the modern SI unit, while mho (ohm spelled backward) is the older term, now largely obsolete. 1 S = 1 mho, but "Siemens" is the unit accepted in the SI system.
4. What is the unit of conductivity in chemistry?
In Chemistry, conductivity is commonly measured in S/cm (Siemens per centimetre) or μS/cm (microSiemens per centimetre), especially for solutions. For standardized measurements and SI, Siemens per metre (S/m) is used.
5. What is the formula of conductivity?
The formula for conductivity (κ) is:
κ = G × (l / A)
where:
• G = conductance of the solution (in Siemens, S)
• l = distance between electrodes (in metres)
• A = area of cross-section of the electrodes (in m2)
The resulting unit is Siemens per metre (S/m).
6. What is μS/cm in conductivity measurement?
μS/cm (microSiemens per centimetre) is a common practical unit for measuring conductivity, especially in water and dilute solutions. 1 S/m = 10,000 μS/cm. This is widely used for testing drinking water, environmental samples, and laboratory solutions.
7. How do you convert the unit of conductivity from S/m to S/cm?
To convert conductivity from S/m to S/cm:
• 1 S/m = 0.01 S/cm
• To convert S/m to S/cm, multiply by 0.01
• To convert S/cm to S/m, multiply by 100
Example: 2 S/m = 2 × 0.01 = 0.02 S/cm
8. What is the difference between conductivity and conductance?
Conductance (G) is the measure of how easily electricity flows through a specific component, with SI unit Siemens (S). Conductivity (κ) is an intrinsic property of a material, defined per unit length and area, with SI unit S/m.
- Conductance depends on object size and shape.
- Conductivity is independent of size, only depends on material nature.
9. What is the unit of molar conductivity?
The SI unit of molar conductivity is S·m2/mol (Siemens metre squared per mole). In practice, it is often given as S·cm2/mol, especially in Chemistry exams and laboratory usage.
10. How are conductivity and resistivity related?
Conductivity (κ) and resistivity (ρ) are reciprocals of each other.
• κ = 1 / ρ
• ρ = 1 / κ
Resistivity has SI unit Ω·m, while conductivity uses S/m.
11. What materials have high conductivity?
Metals, such as copper, silver, gold, and aluminum, have high electrical conductivity. Non-metals, such as rubber or glass, have very low conductivity and act as insulators.
12. Why is conductivity measurement important in solutions?
Conductivity measurement helps determine the concentration of ions in a solution, assess water purity, monitor chemical reactions, and is used in analytical chemistry, water treatment, and environmental studies. High conductivity indicates more dissolved ions; low conductivity suggests purer or less ionic content.
