Question

A beam of monochromatic light goes from material 1 with index of refraction n1 into material 2 with
index of refraction n2. The frequency of light in material 1 is f1 and in material 2 is f2. What is the
ratio of f1/f2?
n1/n2
n2/n1
1
The values of n1 and n2 must be known to find the answer.

Please explain

Answer 1

The answer is 1.

The frequency of light doesn't change when it goes from one medium to another.

What actually happens->

When a light beam travels, it has a wavelength, a frequency and a speed. These three are related by the equation v = f * w.

Here, v = velocity of the light beam in the medium through which it is travelling, w = wavelength of the light beam in that medium, f = frequency of the light beam.

So when a light beam goes from one medium to another, it's velocity changes. While going from rarer to a denser medium, it's velocity decreases, and hence the light beam bends and moves towards the normal line. While going from denser to a rarer medium, it's velocity increases and hence the light beam bends and moves away from the normal line. When the speed of light decreases, it's wavelength increases and when the speed of light increases, it's wavelength decreases. In both cases, the frequency remains constant(as we can see by the equation given above)

Thus, the change in wavelength because of the change in speed is such that the frequency of the light beam can remain constant.