Diffraction grating and scattered light

A few days ago I showed the early results for the spectroscopy demonstration I’m working on for my instrumental analysis class. I passed scattered light and collimated light (using an educational kit from Amazon) through a diffraction grating (also from Amazon) and showed that the results were very different. I posed the question in my vlog for my students: why does the scattered light show up as an image of a rainbow while collimated light shows a rainbow projected onto the paper in front of the grating?

Here’s the answer (if you don’t want to watch the answer in video form). collimated beams create a set of collimated rays of different colors which scatter from the paper.

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Scattered light can be seen at different angles through the diffraction grating from the same location, so looks like an image of a rainbow.

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For a more thorough explanation, I hope you’ll check out the video.

In other news, a Science News report brought my attention to a hand centrifuge capable of 100,000 rpm. The original paper in Nature from the Prakash lab at Stanford is everything I love about open source science. It’s thorough, beautifully presented, and easily replicable.