Question

It is given in most books that color of light is a subjective quantity related to its wavelength. However , it is said that color of light does not change when it refracts from one medium to another , but its wavelength certainly changes as per the formula:
$l'= \frac{l}{u}$.
So if red light of wavelength 7.8 A travels to glass of R.I. 1.5 . So it should change its wavelength to 5.2 A and be blue-green in color . But it is not so. Why?

Answer 1

It is a common misconception that lights color is always dependent on its wavelength . But this is true only if the light is traveling through one medium such as air . If the light enters another medium, such as glass, then the wavelength will change, even though the color will remain the same .

Color always is dependent upon the light's frequency which is the number of waves of light that pass a given plane in space per second . What changes when light goes from one medium to another are both speed of the light and wavelength of the light. But the frequency of the series of light waves does not change. Therefore, the color doesn't change .