# Why do the constituent of white colour have different wavelength?

When white light passes through a prism,it is splitted into its constituents colours due to the difference in the speed of different colours in prism.the colour which has more speed is deviated most(red)and the colour having less speed deviates least(violet).thus,white light is splitted.
we know that wavelength is directly proprtional to speed. The question is why the wavelength of different colours differ from each other?and why does the wavelength of red colour is longest and of violet colour is shortest?

kelseymh3 years ago
"We know that wavelength is directly proportional to speed." That's not correct.

The fact that red is long wavelength and violet is short is just definition. The word names are mapped to the wavelengths based on our perception.

If you're asking why they get bent by different amounts in passing from air to glass, that is because the index of refraction of glass is not a constant, but is rather a function of wavelength (or better, a function of frequency). In particular, the index of refraction is higher for violet (so it is slowed down more in glass, and gets bent more), and not so high for red (so it is not slowed down as much, and gets bent less).

The general rule is that the index of refraction increases with frequency, as in glass, water, diamond, etc., but that is not universally true.
Kiteman3 years ago
It's not "speed" which splits light as it passes through a prism, but the angle at which they are refracted.

That angle depends on the wavelength.
3 years ago
It's both. The index of refraction is just the ratio of speeds of light in vs. out of the medium. Since that index is wavelength dependent, you get different bend angles as a function of wavelength.
3 years ago
Actually it IS speed....
3 years ago
>doh<
steveastrouk3 years ago
(removed by author or community request)
3 years ago
I'm a bit confused here, Steve. If N is independent of wavelength, then you get the same bend angle for all wavelengths, and consequently no spread (dispersion) of the output beam. The only reason a prism can make a "rainbow" at all is dispersion. What am I missing?
3 years ago
Erm radio waves are light, just not in the region visible by humans
3 years ago
Isn't that the exact point I was making ?
orksecurity3 years ago
Note that wavelength is only directly proportional to speed when frequency stays constant. The frequencies of different colors of light are different.
3 years ago
Except speed here is constant, axiomatically
3 years ago
That's my point; the assertion that the two values are proportional made an assumption which isn't true.
seandogue3 years ago
I'm sorry, what source? Do you mean the sun? The incandescent light bulb in your kitchen? The flourescent bulb?

After all, it's not magic, regardless of any personal desire for it to be.

The "white" light is not "white" at all. instead that is our perception as the constituent wavelengths from the "source" are dithered by our eyes and brain.

God, but I wish people would stop being so damned mystical and trying to make science into magic.
rickharris3 years ago
Ah - Octarine!
orksecurity3 years ago
There was a recent question here on Answers where we went into a fair amount of detail on this (correcting my failed memory of freshman physics in the process)...