4 year ago, i saw a CD and noticed rainbow type colors on its surface.
then i started looking into it because um, the curiosity of human
so what is actually happening?
We can not see the single grooves with our eyes because they are too small to be seen by naked eyes.
The grooves make the light spread out into different directions. This is called diffraction.
Diffraction is basically when light spreads out after it hits something . in a CD, the tiny grooves are what makes the light spread.
white light is actually a combination of 7 different colors
↓
RED → ORANGE → YELLOW → GREEN → BLUE →
INDIGO → VIOLET
The CD is basically seperating the colors that are inside the white light.
what is wavelength?
Red light has a longer wavelength, while blue and violet have shorter ones.
but why does it look like a rainbow?
White light have lots of different colors inside it as written above. every color have a different wavelength, so the grooves on the CD send the colors in different directions.
That is why we can see all those colors on the CD instead of just seeing normal white light.
the important thing is diffraction
The grooves on a CD act like a diffraction grating. diffraction grating is basically something with lots of very small lines or grooves that are close together.
when the light hits the grooves, the light waves interact with each other. Some waves add together and some cancel each other. this is called interference.
so what is interference?
We cant see this part happening directly with our eyes, but it helps decide which colors we see from the CD.
why does the rainbow move?
Thats also why the colors change when you tilt the CD. You are changing the angle of the light so the colors are going into different directions too.
If you move the CD a little bit the rainbow can move across the surface. One color might become stronger while another one almost disappears.
I think this is probably the coolest part. It looks like the CD is changing its colors.
CDs make rainbow colors because the tiny grooves on the CD diffract white light and separate it into different colors.
The grooves are basically acting like a diffraction grating. The different colors have different wavelengths so they get sent into different directions.
The colors are already there in the white light. The CD is basically just splitting them apart so we can see them.
kinda cool.