For a metallic conductor, what is the relation between current density (J), conductivity `(sigma)` and electric field intensity E? 

Explanation

To derive the relation between current density (J), conductivity (σ), and electric field intensity (E) for a metallic conductor, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Conductivity and Resistivity**:
- The conductivity (σ) of a material is defined as the reciprocal of its resistivity (ρ). Therefore, we can express this relationship as:
\[
\sigma = \frac{1}{\rho}
...