dispersiongeometric-opticsopticsreflectionrefraction
I was studying the phenomena of the formation of a rainbow. In my book, the following diagram is given:
So, the rays at the red end of the spectrum make a larger angle with the incident ray than the rays at the violet end of the spectrum. However, whenever we see a primary rainbow, the red is always on the top.
Why is it so? I know there is an obvious explanation and I am surely going wrong somewhere in my understanding. Please help me understand my mistake.
You are seeing only one color from each droplet. Even though each droplet reflects the whole spectrum, only one color gets to your eye. The rest of the light from a single droplet is sent somewhere else than your eye (maybe into the eye of someone standing near you). So if you see a thick blue band in a rainbow, the blue band is formed by many reflections from many droplets. You cannot see many thin rainbows (each one from a single droplet), because each droplet contributes to your complete rainbow image as one "pixel" only, in a sense.
Each individual droplet reflects a whole cone of light - a complete circular rainbow (the image below has only 2 colors for clarity, but you get the idea - see this video):
All droplets in a rain reflect a huge amount of these cones (circular rainbows), but you can see only a small fraction of every cone from each droplet. All these fractions sum into the rainbow you see. So - how is the vertical portion of a rainbow formed? Simply - it is formed by the rays from the vertical portions of the light cones reflected by the droplets that are located in the direction where you see the vertical portion of the rainbow.
Again - the rays that you do not see are sent somewhere else. You can see them if you move around, but then you cannot see the rays that you were seeing in your previous location.
That means that a single cone from a single droplet can contribute to different parts of different rainbows, seen by different people: it can contribute to the upper horizontal part of a rainbow seen by you (that would be a color ray from the lower section of that individual cone), but at the same time it can contribute to the vertical portion of a rainbow seen by someone else who is higher and to your left (that would be a color ray from the left vertical portion of that individual cone).
It just means that the path of the light intersects the plane of the glass. The angle between this ray and the perpendicular or normal to the surface is the angle of incidence. The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface.
Best Answer
Yes. It is precisely the larger angle that makes this happen. Because the red is angled "down" more the red droplets are the ones located higher in your field of view.