When visible light travels through a medium such as glass or water, several phenomena occur, including a change in speed, wavelength, and direction. These changes are a result of the interaction of light with the atoms or molecules in the medium.
Change in speed: When light enters a medium, it slows down. The speed of light in a vacuum is approximately 299,792 kilometers per second (km/s), but it travels slower through materials. The speed of light in glass is typically around 200,000 km/s, and in water, it is about 225,000 km/s. This decrease in speed is due to the interaction of light with the electrons in the atoms or molecules of the medium.
Change in wavelength: As light travels through a medium, its wavelength can change. This phenomenon is known as wavelength-dependent refraction or dispersion. Different wavelengths of light interact differently with the medium, causing them to bend or refract at different angles. This results in the separation of light into its constituent colors, as observed in a prism. This effect is responsible for phenomena such as rainbows.
Change in frequency: The frequency of light remains constant when it travels through a medium. Frequency represents the number of wave crests passing a given point per unit of time. In a vacuum, the frequency of light does not change. However, since the speed of light changes in a medium, the wavelength changes as well. The frequency and wavelength are inversely proportional, so as the wavelength changes, the frequency remains constant.
In summary, when visible light travels through a medium like glass or water, it changes speed, wavelength, and direction due to interactions with the atoms or molecules in the medium. These changes are responsible for phenomena such as refraction, dispersion, and the bending of light rays.