Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: lancenti on 13/05/2009 12:23:52

Title: Does the frequency of light change when it refracts?
Post by: lancenti on 13/05/2009 12:23:52

I was just wondering...

Refractive Index, n, is defined by

n = c / v

where c is the speed of light in a vacuum, and v is the speed in the medium.

Now, since light is a wave, we look at v = fλ.

So when light refracts, it slows down but then is it the frequency that changes, the wavelength that changes or both?

Title: Does the frequency of light change when it refracts?
Post by: lyner on 13/05/2009 12:39:01

The frequency can't change, basically because the fields have to be going up and down 'in step' at the boundary.
This is common for all waves when they hit interfaces between two 'media' . Imagine a particle at the boundary between two media;  if the 'in' and 'out' frequencies were different, it would have to be in two places at once, most of the time. For particles on either side not to be in step would require some energy to change things and where would it come from?
The wavelength, on the other hand can be anything because you still have continuity over the interface.
It's the same argument for electromagnetic waves but it's fields as well as particles which are involved in the discussion so it's more complicated.