CD's have little bumps on them that act like a grating right?

[UrbanXrisis]

CD's have little bumps on them that act like a grating right? but how is it that the little bumps can split white light into the rainbow of colors when I look at it?

 

[Doc Al]

Think of the many grooves as forming a diffraction grating. Each color creates a diffraction pattern at a slightly different angle, thus producing a rainbow effect.

 

[UrbanXrisis]

how does each color create a different diffraction pattern? do you mean light seen from different angles become different colors due to diffraction?

 

[Doc Al]

Different colors will diffract at different angles. (Ordinary light is a mix of colors.)

 

[UrbanXrisis]

so say I was in the nanometer world and I am sitting on one of the CD 'bumps.' I view white light coming towards the CD and then depending on where it hits, it bounces off in a different direction due to the 'bumps'. The light that bounces off constructively and destructively interfers to create different colors. how is looking at a CD from a different angle going to change the color of the CD when the constructive and destructive interference of the light have already created a certain color? why would a color change just because it bounces off the same bumps but from a different angle?

 

[Doc Al]

Think of it this way. If there was no diffraction, then the different colors in the white light would reflect at the same angle and the colors would not be visible to the eye. But on the CD, each color diffracts at a slightly different angle. When you look at the CD, each spot on the CD makes a different angle with your eye, thus reflects a different color. (Note that each spot reflects all colors, but you only see one of them depending on the angle that it makes with your eye.) Make sense?

 

[Smilecdl]

different coloured light has different wavelengths and therefore scatters by a different amount

 

[UrbanXrisis]

Think of it this way. If there was no diffraction, then the different colors in the white light would reflect at the same angle and the colors would not be visible to the eye. But on the CD, each color diffracts at a slightly different angle. When you look at the CD, each spot on the CD makes a different angle with your eye, thus reflects a different color. (Note that each spot reflects all colors, but you only see one of them depending on the angle that it makes with your eye.) Make sense?

how does the little bumps on the CD split light into different colors?

 

[Doc Al]

Read up on how diffraction gratings work. Start here: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/grating.html

 

[UrbanXrisis]

but why does refraction gratings work the same way as diffraction gratings?

 

[Doc Al]

What do you mean by "refraction" grating?

 

[UrbanXrisis]

instead of light going though slits, it is reflected

 

[Doc Al]

Ah, you mean reflection grating (as opposed to transmission grating). To see a diffraction pattern, all you need is a regular pattern of light sources with the appropriate phase relationship. It doesn't matter if these light "sources" are due to transmission or reflection.