Quote:
Originally Posted by paul m
I suppose that the 'extra' arcs are due to a double diffraction of light from the initial one - the colours come out in reverse order to the primary rainbow. Anybody understand the physics?  |
Hi Paul,
The 'extra' arcs, as you put it,
are formed by a different diffraction angle than the main arc.
The main one is formed by a dubble diffraction; one caused when entering the waterdrop and the second when the light leaves the drop. They are also reflected by the back of the raindrop and when the red light is diffracted it makes a angle of 42 degrees. Red travels the smallest distance while blue travels the furthest. This means that red stays closer to the sun; so that is why red is the outer colour in the primary rainbow.
The extra arcs that are formed under go a second reflection caused by the inside of the water drop. Each reflection causes a decrease in light, so that's is why the extra arcs are less bright than the main one.
The colours are in reverse order because the light is defracted at a different angle due to the extra reflection. The light now undergoes diffraction in an angle of 51 degrees. Red still has to stay closest to the sun and there for ends up under in the spectrum.
As I didn't think my explanation wasn't the clearest, I decided to draw it!
~*~Frostfire~*~