When white light is sent through prism, it is split into colors. A great discovery by Newton. Raindrops acts like a prism and split sun light into seven colors forming the rainbow in the sky.
Let us go deeper into this phenomenon.
Take two carbon pencils (rods) both should be sharpened at one end. Connect positive of high voltage to one rod and the negative to another. Place the two pencils face to face so that there is a little gap between the sharpened ends.
Now powerful white spark will appear in the gap. Actually carbon pencils burn. This set up is called 'carbon-arc lamp' used as a light source in old cinema film projector.
If this light is sent through the prism, it split into spectrum of colors. Since the light comes from carbon atoms, the colors can be called carbon spectrum. (see photo). The pattern of colors is unique to carbon. No other element will give out same arrangement of colors. The spectrum is like finger print of the element carbon.
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| famous double lines of sodium |
We can extract spectrum from all the elements in the periodic table. For example, we know sodium lamp, gives out yellow light. If it is sent through the prism, it split into two yellow colors known as sodium doublet. (yellow in two wavelength). So it is the 'ID' of sodium.
Since light and spectrum is the atomic phenomenon, the colors reveal information about atomic structure of the element(arrangement of electron).
Sunlight gives out spectrum called 'solar spectrum' using which we can study the sun's atmosphere. We can find out the elements present there.
It is possible to form spectra from star light. It can yield info.about the star.
If the source of light moves, the position of colors in the spectrum shifts, called Doppler shift. Using Doppler shift, the speed and direction of any moving source of light, (for example a star) can be calculated.
Next time , when you see colors in a rainbow, in a soap bubble, in a water fall, remember they hold so much knowledge.
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