![]() They wrap around the top of the sky, and the bright bands are seen on the opposite side of the center of the cone with the colors upside down.These behaviours of waves can help us understand how water waves interact with land. Note: The cones making the secondary rainbow are about 125° to 130° wide. We see it as violet because it is brighter but is a paler violet than you would see in a spectrum. Violet's cone is narrowest, and it is mixed with all the other colors. Red's cone is widest, and its band is seen on the outside (see note below) of the rainbow, where no other colors are seen. (1) The outer edge of the cone is much brighter than its interior and appears as a bright band and (2) The width of the cone is different for each color due to dispersion. Two effects related to this cone cause rainbows. If the number is odd, the center of this cone will be straight back towards the sun if even, it will be in the same direction as the original light. ![]() When you consider all of the light hitting the drop - something most explanations do not do - you will see that the light will be spread out into a cone of light that depends on the color and number of internal reflections. It refracts both times it crosses the boundary. Rainbows are caused by light that enters a raindrop, reflects one or more times internally (not TIR), and exits. Since that is what "reflection" means, it is redundant. So "internal" does not refer to inside an object, it only refers to inside the first medium. But it's also what makes air bubbles in water appear shiny when it happens on the outside of the bubble. It's what makes diamonds sparkle, and fiber-optic cables work. This is called Total Internal Reflection, or TIR. Dispersion is still happening, but is separation?Īt large angles, transmission can't occur when light tries to leave a denser material like water and enter a sparser one like air, because Snell's Law has no solution. But shine the full sun on that prism, and you get a smear of mostly white light. A prism can separate a pinhole or slit of light into the individual colors, called a spectrum. Under controlled circumstances, like sunlight passed through a pinhole or a slit, dispersion causes separation of colors. This results in dispersion, which means only that even though you could ignore color in the first medium, you can't in the second. The refraction is different for each color of light. This change is called refraction, although sometimes that word is incorrectly used to mean transmission. It changes direction according to Snell's Law. Transmission means the light enters the second medium. There are two kinds: specular, which reflects in a single direction described by the Law of Reflection and diffuse, which reflects in many directions. Reflection means it bounces off the boundary, and stays in the first medium. Reflection and Transmission refer to what happens when light traveling in one medium encounters a boundary with another. It has nothing to do with true rainbows, but some rainbow-like effects ( glories) are caused by diffraction. Being more careful with the words eliminates these problems.ĭiffraction refers to specific kind of interference of light waves. But it happens several ways in a naive explanation of rainbows that, while completely incorrect, nevertheless gets taught in schools. Sometimes this is completely wrong, and other times it is just incomplete and misleading. Frequently these words and phrases get tossed around carelessly, and sometimes interchangeably. Diffraction, interference, refraction, reflection, diffuse reflection, specular reflection, transmission, dispersion, separation of colors, internal reflection, total internal reflection, spectrum, rainbow, etc.
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