When light travels through a medium, such as water, how does its speed compare to that in air?

When light travels through different media, its speed changes depending on the optical properties of those materials. In the case of water, the speed of light is slower compared to its speed in air. This reduction in speed is due to the refractive index of the medium. The refractive index of water is higher than that of air, indicating that light will slow down as it enters water from air.

The refractive index is a dimensionless number that describes how much light slows down in a medium compared to vacuum or air. For instance, the refractive index of air is approximately 1, while for water, it is around 1.33. This means light travels approximately 1.33 times slower in water than it does in air, leading to a decrease in speed as it transitions from one medium to the other.

Users of this information should understand that as light moves from a less dense medium (like air) to a denser medium (like water), it slows down, which is a fundamental property of wave propagation in different materials.