The speed of light does change when it passes through a medium, such as a metal. In a vacuum, light travels at a constant speed, denoted by the symbol "c," which is approximately 299,792,458 meters per second.
However, when light enters a different medium, such as a metal or any other transparent material, its speed is reduced. This reduction in speed is due to the interaction of light with the atoms or molecules of the medium.
In a transparent material like glass or water, for example, the speed of light is typically lower than the speed in a vacuum, but it is still quite high. The reduction in speed is governed by the refractive index of the material, which is a measure of how much the speed of light is reduced when it enters that medium.
Metals, on the other hand, behave differently when it comes to the propagation of light. Metals are highly reflective and conductive materials due to the presence of free electrons. When light interacts with a metal, it can induce oscillations of these free electrons, leading to a phenomenon called plasmons.
In metals, the speed of light is significantly reduced compared to a vacuum or transparent materials. The reduction in speed depends on various factors, including the metal's properties, the wavelength of light, and the characteristics of the metal's electron system.
In summary, when light passes through a medium, such as a metal, its speed is generally reduced compared to its speed in a vacuum. The specific reduction in speed depends on the properties of the medium and can vary for different materials.