Finding a light source that produces an absorption spectrum?

[Persimmon]

This is an observational exercise where I have to find several different light sources and observe their spectra through a diffraction grating, then record my observations. I need two sources of each (i.e. continuous, emission, absorption).

Continuous and emission are fairly easy, but for the life of me I can't think what I could observe that would produce an absorption spectrum. I know that absorption spectra come about when there is an absorbing material like cool gas in front of a black body but I don't really know how I could find something like that. I thought maybe if I looked at a light source from far away in cold weather that might do it, but I still didn't see an absorption spectrum. Any help or hints would be much appreciated!

 

[ehild]

The sun itself produces absorption spectrum of its outer atmosphere: http://en.wikipedia.org/wiki/Fraunhofer_lines.

You can make a "light source" showing absorption spectrum by placing a coloured liquid (solution of some dye, or solution of KMnO4...) in front of a simple tungsten lamp.

ehild

 

[Persimmon]

Brilliant, thanks! I hadn't thought of that. I feel a bit stupid now.

 

[ehild]

Or it can be a colour filter glass or a simple coloured glass in front of the tungsten lamp...


ehild

 

[Nickie]

Thank you for reaching out about your observational exercise. It is great that you have a good understanding of continuous and emission spectra. Let me provide some guidance on how you can observe an absorption spectrum.

Firstly, let's define what an absorption spectrum is. It is a spectrum of electromagnetic radiation transmitted through a substance, showing dark lines or bands due to absorption of specific wavelengths. This means that the light source you are observing needs to have a substance in front of it that is capable of absorbing certain wavelengths of light.

One way to find an absorption spectrum is to use a gas discharge tube. These tubes contain a specific gas at a low pressure and can emit light when an electric current is passed through them. When you observe the spectrum of this light through a diffraction grating, you will see dark lines or bands where the gas has absorbed specific wavelengths. This is because the gas atoms have absorbed the energy of those wavelengths and re-emitted them in different directions, resulting in a dark line in the spectrum.

Another way to observe an absorption spectrum is by using a spectrophotometer. This instrument measures the amount of light absorbed by a substance at different wavelengths. You can use different substances, such as colored liquids or solutions, and observe their absorption spectra using the spectrophotometer.

I hope these suggestions help you find a light source that produces an absorption spectrum. Remember to always be curious and open to trying new methods in your scientific experiments. Best of luck!