Define dielectric constant of a medium. What is its S.I. unit?

The dielectric constant of a medium, also called the relative permittivity, is a measure of a material's ability to store electrical energy in an electric field. It is the ratio of the electric field in a vacuum (or air) to the electric field in a particular medium when both are subjected to the same applied voltage. In simpler terms, it shows how much a material can reduce the force between two charges compared to the force in a vacuum.

Mathematically, the dielectric constant (K) is expressed as:

K = ε / ε₀

Where:

ε is the permittivity of the material.
ε₀ is the permittivity of free space (vacuum), which is a constant with a value of 8.854 × 10⁻¹² C²/N·m².
The dielectric constant is a dimensionless quantity, which means it has no units. It is a pure number that compares the permittivity of the material with the permittivity of free space.