# Water changing wave length

The Baron
I have a question, say a wave of light is emitted, and it passes through water, changing it's wave length to 380nm inside the water, once it comes out of the water, to vacuum will the wavelength remain at 380nm or will it change?

## Answers and Replies

Mentor
The wavelength (and speed) changes as the light passes through various media. What remains the same is the frequency.

sophiecentaur
Science Advisor
Gold Member
once it comes out of the water, to vacuum will the wavelength remain at 380nm or will it change?
I think this must be one of the most frequently asked questions in Physics. Strange - but not so strange is that we all accept the fact that sound doesn't change frequency as it passes through different media. Where's the difference between the two ideas? Imo, it has to be because we started off (and still do, largely) by quantifying light in terms of its wavelength but we hear the frequency of sound.
The clever bit is about a change in wave speed affecting the wavelength and not the frequency is one step further on in our Physics education. Frequency is the fundamental quantity in waves because the vibrations have to be 'continuous' at an interface (the ups and downs cannot get out of step across a boundary). The wavelength is then tied to the frequency by the wave speed.