Question

When monochromatic light travels from one medium to another its beginning changes that we can see remains the same explain?

Answer 1

Frequency (energy also) remains same.

This is because, when light moves from one medium to another, the particles of the medium start vibrating with the same speed that is with speed of light.

Answer 2

The monochromatic ray of light deviates in the second medium towards or away from the normal if there is any change in the refractive index of the second medium.

If the refractive index of the first and the second medium are same, then the light ray passes undeviated.

However,
The frequency remains same in both the cases.