Diffraction Gratings: Understanding Spectroscopes Using Pringles Tubes

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In summary: CD so that it fits inside the lid of a pringles can. He has some idea of how it works, but would like to know more about it. Under different angles, Dave can see the different line spectra that are caused by the interference of waves that are half a wavelength out of phase.
  • #1
Jimmy87
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Hi, I recently made a spectroscope using a pringles tube. I basically cut a very narrow slit at the metal end and at the plastic lid end I cut a circular shape out of a CD so that it fits inside the lid (I had to strip off the silver lining of course). I have some idea of how it works but would greatly appreciate some clarification and any extra information. Take the case of a sodium lamp that gives discrete spectral lines. As I understand it the light comes from the sodium lamp through the narrow slit and hits the CD inside the lid. The grooves on the CD reflect light at different angles depending on the wavelength which therefore split the light up. Since the silver surface is stripped off these reflected waves can transmit through into your eye. A couple of things I don't quite understand:

1) From what I have read, the reflected light rays can interfere constructively or/and destructively. So would you therefore not necessarily be seeing all the line spectra as some may have interfered destructively between the CD and your eye (if they were half a wavelength out of phase).

2) It also says that what you are seeing as line spectra are actually images of the slit. Is that right? Surely the light just comes through the slit, there's no image being formed is there?
 
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  • #2
Jimmy87 said:
The grooves on the CD reflect light at different angles depending on the wavelength which therefore split the light up.
It is diffraction, not reflection.
Jimmy87 said:
So would you therefore not necessarily be seeing all the line spectra as some may have interfered destructively between the CD and your eye (if they were half a wavelength out of phase).
You see exactly the points where they are in phase. Under different angles you don't see light of this specific wavelength.

Jimmy87 said:
2) It also says that what you are seeing as line spectra are actually images of the slit. Is that right? Surely the light just comes through the slit, there's no image being formed is there?
Well, you still have the finite size of the slit and the light source that will give a finite width/height of the light patterns.
 
  • #3
The light coming in through the slit forms a narrow, rectangular 'column' approximately the same size of the slit. When this column of light hits the CD, the grooves separate the different wavelengths and the column, as a whole, spreads out. So the line spectra look like the slit only in the sense that the length and width correspond to that of the slit. So a very narrow slit vies you narrow lines, while a wide one gives you wide lines.
 
  • #4
mfb said:
It is diffraction, not reflection.
You see exactly the points where they are in phase. Under different angles you don't see light of this specific wavelength.

Well, you still have the finite size of the slit and the light source that will give a finite width/height of the light patterns.

Thanks for the answers. I thought the light hits the grooves and different wavelengths reflect at different angles? So how is the light splits up if it not reflected. How is diffraction defined?
 
  • #5

What is a diffraction grating?

A diffraction grating is an optical component that is used to separate light into its different wavelengths, producing a spectrum. It consists of a large number of parallel, closely spaced lines or grooves on a surface, which act as a series of parallel slits that diffract the light passing through them.

How does a diffraction grating work?

When light passes through a diffraction grating, the waves are diffracted by the lines or grooves on the surface. This causes the light to spread out into its component wavelengths, creating a spectrum. The amount of diffraction depends on the spacing of the lines or grooves, with smaller spacing resulting in a larger separation of wavelengths.

What is the purpose of using Pringles tubes in understanding spectroscopes?

Pringles tubes can be used as a simple and inexpensive way to create a diffraction grating. By cutting parallel slits into the metal bottom of the tube, it can act as a grating and produce a spectrum when light is shone through it. This can be a fun and hands-on way to understand the principles of spectroscopy.

What can diffraction gratings be used for?

Diffraction gratings are commonly used in spectroscopy to analyze the composition of light sources, such as stars or chemical samples, by separating the different wavelengths of light. They are also used in various other applications such as telecommunications, laser systems, and optical instruments.

How do diffraction gratings compare to other types of spectroscopes?

Diffraction gratings are just one type of spectroscope, with other types including prisms and filters. Diffraction gratings are preferred for their ability to produce a high-resolution spectrum and their versatility in being able to analyze a wide range of wavelengths. However, they are limited in the amount of light they can transmit, so other types of spectroscopes may be more suitable for certain applications.

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