Electric flux density, often denoted as **D**, is a vector quantity. It represents the distribution of electric field lines in a material and is defined in terms of the electric field **E** and the permittivity of the medium.
### Definition
The electric flux density is defined by the equation:
\[
\mathbf{D} = \epsilon \mathbf{E}
\]
where:
- **D** is the electric flux density (in coulombs per square meter, C/m²),
- **ε** (epsilon) is the permittivity of the material (in farads per meter, F/m),
- **E** is the electric field strength (in volts per meter, V/m).
### Characteristics of Electric Flux Density
1. **Vector Nature**: Since both **D** and **E** are vectors, **D** inherits this property. It has both magnitude and direction, indicating how electric field lines distribute through a given area.
2. **Relationship with Charge**: Electric flux density is related to free charge density (\(\rho_f\)) in a dielectric medium via Gauss's law in differential form:
\[
\nabla \cdot \mathbf{D} = \rho_f
\]
This relationship illustrates how **D** can be used to analyze electric fields generated by free charges.
3. **Dependence on Medium**: The vector **D** is affected by the medium through which the electric field travels. In isotropic materials, it is directly proportional to the electric field **E**, while in anisotropic materials, the relationship can become more complex due to directional dependencies.
4. **Applications**: Electric flux density is crucial in various applications, such as capacitor design, analyzing electric fields in different materials, and studying electromagnetic waves in dielectric media.
### Conclusion
In summary, electric flux density is a vector quantity that encapsulates how electric fields interact with materials. Its vector nature allows it to provide important insights into both the magnitude and direction of electric field distributions, making it a fundamental concept in electromagnetism and electrical engineering.