When an electromagnetic wave transitions from free space to a lossless medium with a refractive index greater than one, its wave impedance decreases due to the relationship between impedance, speed of light, and refractive index. The wave impedance in free space is defined as η₀, while in a medium, it is modified by the refractive index n, resulting in η = η₀/n. This reduction in impedance can be intuitively understood as the wave encountering a medium that slows it down, leading to a higher density of energy in the medium compared to free space. Consequently, the wave's ability to propagate is altered, resulting in a smaller impedance value. Understanding this concept is crucial for analyzing wave behavior in different media.
