When light travels from one medium to another, the frequency of the light wave remains constant. The frequency of light refers to the number of wave crests (or troughs) that pass a given point in a unit of time. It is measured in hertz (Hz).
According to the wave theory of light, the speed of light changes when it passes through different mediums, and this change in speed causes the light to refract or bend. However, the frequency of the light wave itself remains the same. This principle is known as the conservation of frequency.
The wavelength and speed of light can change when it enters a different medium, but the frequency remains constant. The equation that relates the speed of light (v), wavelength (λ), and frequency (f) is:
v = λ × f
Since the frequency remains unchanged, any change in the speed of light will be accompanied by a corresponding change in the wavelength to satisfy this equation.