Yes, the speed of light does change when it passes through different media. In a vacuum, such as outer space, light travels at a constant speed of approximately 299,792,458 meters per second (or about 186,282 miles per second).
However, when light passes through other materials, such as glass, water, or air, its speed is reduced. This reduction in speed is due to the interaction of light with the atoms or molecules in the material. These interactions cause the light to be absorbed and re-emitted by the atoms or molecules, which leads to a delay in its propagation.
The speed of light in a medium is typically denoted as "v" and is given by the equation v = c/n, where "c" represents the speed of light in a vacuum and "n" represents the refractive index of the medium. The refractive index is a property of the material and is a measure of how much the speed of light is reduced when it enters the material.
Different materials have different refractive indices, which means they affect the speed of light in different ways. For example, the refractive index of glass is typically higher than that of air, so light slows down more when it enters glass compared to when it passes through air.
It's worth noting that the speed of light in a medium is still extremely fast compared to everyday objects and is often considered "close enough" to the speed of light in a vacuum for many practical purposes. However, the change in speed does have important consequences in various fields, such as optics, telecommunications, and the study of light interactions with matter.