Question

which of the following characteristics of light remains unchanged when light gets reflected

Answer 1

In many cases, people always ask about a common thing, why the frequency is not changed while other parameters do. Such as in this case, or in the case of stepping up or down the voltage of AC with the help of a transformer, or sound passing through two different media.

One thing to be noted in the case of frequency, that it depends upon time. If time gets diaiated/elongated or contracted/shortened in any action, then it would happen. If the time taken by light to enter the glass medium be less than the time taken by it to come out, then the number of waves being same and time shortened, so the frequency would be higher in glass medium. But that's not possible. So the frequency remains same in such cases.

Let us take the case of Doppler effect of sound. When the source and observer approaches each other, the time taken by sound to travel the distance between them is shorter than the duration of its production. So the duration to hear a number of waves is less than the time taken to produce it. So the frequency heard is higher than original.

So, In any process, when time is unaffected, the frequency of the observed quantity remains same.

Hope this helps.