Final answer:
When a light wave enters into a medium of different optical density, its speed and wavelength change, but its frequency remains the same.
Step-by-step explanation:
When a light wave enters into a medium of different optical density, its speed and wavelength change, but its frequency remains the same.
According to the equation v = fλ, where v is the speed of light, f is the frequency, and λ is the wavelength, since the frequency remains constant, if the speed decreases, the wavelength must also decrease to maintain this equation.
For example, when light enters water from air, its speed decreases, causing its wavelength to become shorter. However, its frequency remains unchanged.