When light passes from one medium to another, such as from air to water or from air to glass, it undergoes a phenomenon called refraction. Refraction occurs due to a change in the speed of light as it enters a different medium. The speed of light is different in different materials due to their varying optical properties.
When light encounters a change in the speed of propagation, its wavelength and frequency can be affected. According to the wave theory of light, the speed of light is equal to the product of its wavelength and frequency (v = λf), where v represents the speed, λ is the wavelength, and f is the frequency.
During refraction, the speed of light changes, but the frequency of the light wave remains constant. This phenomenon is known as the principle of conservation of frequency. The frequency of a wave is determined by the source that generates it and does not change as it propagates through different media.
Since the frequency remains constant, but the speed of light changes, the wavelength must adjust accordingly to satisfy the equation v = λf. When light enters a medium where its speed decreases, such as going from air to a denser medium like water or glass, the wavelength decreases. Conversely, when light exits a denser medium and enters a less dense one, the wavelength increases.
To summarize, during refraction, the frequency of light remains constant as it passes from one medium to another. However, the change in the speed of light in different media leads to a change in its wavelength to maintain the relationship between wavelength, frequency, and speed of light.