What happens to the wavelength of light when it travels from air into water?

When light travels from one medium, such as air, into another medium, like water, its speed changes due to the differing densities and refractive indices of the materials. In air, light travels faster than it does in water.

As light enters the denser medium of water, it slows down, which results in a decrease in wavelength. The relationship between speed, frequency, and wavelength is given by the equation:

Speed = Wavelength x Frequency

Since the speed of light decreases as it enters water and the frequency of light remains constant (frequency is determined by the source and does not change when transitioning between media), a decrease in speed leads directly to a decrease in wavelength.

Thus, when light transitions from air to water, the wavelength of the light decreases, confirming that C is the correct answer.