The terms **dielectric constant** and **relative permittivity** are often used interchangeably in many contexts, but they do have subtle differences.
### 1. **Dielectric Constant (ε\(_r\)):**
- **Old Term**: Historically, "dielectric constant" was used to describe the relative permittivity of a material.
- **No Unit**: It is a dimensionless quantity, representing how much a material can store electrical energy in an electric field compared to a vacuum.
- **Symbol**: It is denoted by \( \varepsilon_r \), which is the same symbol used for relative permittivity.
- **Formula**: \( \varepsilon_r = \frac{\varepsilon}{\varepsilon_0} \), where:
- \( \varepsilon \) is the permittivity of the material.
- \( \varepsilon_0 \) is the permittivity of free space (vacuum).
### 2. **Relative Permittivity (ε\(_r\)):**
- **Modern Term**: "Relative permittivity" is the more precise and technically correct term in modern scientific usage.
- **Physical Meaning**: It describes how much the electric field is reduced inside a material compared to a vacuum.
- **No Unit**: Like dielectric constant, it is dimensionless.
- **Usage**: It's typically used in scientific and engineering discussions regarding the material’s electrical properties.
### Key Difference:
- **Dielectric constant** is considered an older or informal term, whereas **relative permittivity** is the precise term used in technical discussions today. They both refer to the same quantity, so in most practical situations, they are interchangeable, but **relative permittivity** is preferred for accuracy.