Question

If a light wave in water has a wavelength of 2 meters, what is its frequency?

Answer 1

\[v=f \lambda\]

\[f=v/\lambda\]

where \[v\] is the speed of light

Answer 2

Be careful here guys.

Remember that the refractive index of a substance is\[n = {c_{vacuum} \over c_{medium}}\]Water has a refractive index of 1.33, therefore, the speed of light in water is\[c_{water} = {c_{vacuum} \over n}\]Therefore, the frequency of the lightwave in water with a wavelength of 2 meters is\[f = {{c_{vacuum} / n} \over 2}\]