Given the wavelength of lightwave in a vacuum is 540mm, what will it be in water, where n = 1.33? To solve this problem, it seems like I would need to find a relationship of the frequency of light to the wavelength and that is easily obtained from the equation lambda = c/nu and the frequency can be solved. Since n=speed of light in vacuum/speed of light in material. We can find the speed of light in the material (water) and thus the wavelength. But it seems like there is a problem somewhere as I cannot seem to obtain a reasonable answer.