# Is frequency of Electromagnetic wave it's intrinsic property?

I was solving a simple refraction problem where the wavelength and velocity of the sodium light needed to be calculated after refracting through glass from air. Now after calculation I found the frequency is same for the both while we know velocity = frequency $$\times$$ wavelength.

So is the frequency being an intrinsic property of EM waves? I know it is pretty simple but could not find a satisfactory answer.

Normally, yes. Some generator provides a wave of a given frequency $$\omega$$, and the other things (wave vectors $$\vec{k}$$, etc.) are calculated depending on the medium where the wave travels.

• What are the exceptions? The first that comes to my mind is gravitational redshift. Do other exceptions exist? – Cuspy Code Jan 13 at 20:58