Insulators are the solid with very low conductivities ranging between A… Here , A refers to

Options

A. `10^4 "to " 10^7 Omega^(-1) m^(-1)`
B. `10^(-20) " to " 10^(-5) Omega^(-1) m^(-1)`
C. `10^(-20) " to " 10^(-10) Omega^(-1) m^(-1)`
D. 10^(-6) " to " 10^4 Omega^(-1) m^(-1)`

Explanation

To solve the question regarding the conductivity range of insulators, we can break it down into the following steps:

### Step-by-Step Solution:

1. **Understanding Conductivity and Resistivity**:
- Conductivity (σ) is the reciprocal of resistivity (ρ). The relationship can be expressed as:
\[ \sigma = \frac{1}{\rho} \]
- Resistivity (ρ) is defined in terms of resistance (R), length (L), and area (A) as:
\[ R = \frac{\rho L}{A} \]

2. **Units of Conductivity**:
- The unit of resistivity (ρ) is ohm-meter (Ω·m). Therefore, the unit of conductivity (σ) is:
\[ \text{Unit of } \sigma = \text{Ohm}^{-1} \cdot \text{m}^{-1} \]

3. **Range of Conductivity for Insulators**:
- Insulators are characterized by very low conductivity values. The typical range of conductivity for insulators is:
\[ 10^{-20} \text{ to } 10^{-10} \text{ Ohm}^{-1} \cdot \text{m}^{-1} \]
- This range indicates that insulators have extremely low ability to conduct electricity.

4. **Understanding the Band Gap**:
- In insulators, there is a significant energy gap between the valence band and the conduction band, usually greater than 3 electron volts (eV). This large band gap prevents electrons from moving freely from the valence band to the conduction band, which is why they exhibit low conductivity.

5. **Conclusion**:
- Based on the above understanding, the answer to the question is that the range of conductivity for insulators is from \(10^{-20}\) to \(10^{-10}\) Ohm\(^{-1}\)·m\(^{-1}\).

### Final Answer:
The value of A refers to the range of conductivity for insulators, which is from \(10^{-20}\) to \(10^{-10}\) Ohm\(^{-1}\)·m\(^{-1}\).

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