Mar 2017

What is Diffraction Grating?

March 3, 2017

Wondering what a diffraction grating is? It’s one of the many topics that makes physics fun and academically fulfilling. Diffraction grating is an important concept covered in our physics tuition and is also the underlying technology around for CDs.

What does a diffraction grating do?

A diffraction grating is used when you need to separate the different spectrum wavelengths of light. Think of it as a ‘super prism’. This means it is the perfect tool to measure atomic spectra for telescopic and laboratory instrumentation. It is the tool of preference for separating the colors of incident light.
The technology is pretty simple- it’s effectively a grid of scratches on plastic. The scratches become opaque but the intervening area can allow light through, turning it into a grid.

How does a diffraction grating do this job?

The core concept of a diffraction grating is actually super simple. Parallel splits, spaced incredibly closely are used. A large number of splits makes a very narrow and sharp, high-resolution split that makes it suitable for spectroscopic applications. While a double slit ‘grating’ is possible to use, it produces less peak intensity [although maximum intensity remains the same].
If you put a light of a single wavelength through a diffraction grating, it will be diffracted as per beam. Different wavelengths will diffract at different angles depending on their diffraction relationship.

How do I use a spectrometer?

Remember that the laboratory diffraction grating is photographic and cannot be touched. Place it with the slits aligned vertically on a table with the glass facing the light source to avoid issues of refraction. The whole table should be aligned to make the grating perpendicular to the incident beam. Adjust for maximum brightness, and look for the second and third order spectra. You can then measure the angles that present.

What are the common world applications of the diffraction grid?

The diffraction grid you are most likely to observe in everyday life is the common CD. The tracks act as diffraction gratings, separating white light into its component colors. There are about 625 tracks per millimeter on a cd, the same with laboratory diffraction grating. A red light on the CD, as per the light which reads them, produces a first order diffraction angle at about 22 degrees.
Joining us for JC physics tuition will prepare you for the world where the science we cover becomes fun!

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