Here's a breakdown:

* Permittivity (ε): This measures a material's ability to store electrical energy. A higher permittivity means the material can store more electrical energy, which slows down the wave.

* Permeability (μ): This measures a material's ability to support the formation of a magnetic field. A higher permeability means the material supports a stronger magnetic field, which also slows down the wave.

The speed of light in a vacuum (c) is a fundamental constant, but when light enters a material, its speed changes. The relationship between the speed of light in a vacuum (c), the speed of light in the material (v), the permittivity (ε), and permeability (μ) is:

v = c / √(εμ)

Key Points:

* The speed of light is fastest in a vacuum, where ε and μ are essentially 1.

* In materials, the speed of light decreases, with the extent of the decrease depending on the permittivity and permeability of the material.

* For example, light travels slower in water than in air because water has a higher permittivity and permeability than air.

Let me know if you'd like more details on any of these concepts!