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Q: science - spectra ( No Answer,   2 Comments )
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 Subject: science - spectra Category: Science > Physics Asked by: bra00424-ga List Price: \$20.00 Posted: 16 Oct 2006 06:25 PDT Expires: 15 Nov 2006 05:25 PST Question ID: 774011
 ```I would like to make cheap simple device to measure the intensity of various wavelengths emitted by the sun (aka spectrometer). It would only need to cover the visible spectrum. With this information, I could use Wein's law to estimate the temperature of the sun by finding wavelength of maximum intensity. Looking for direction or suggestion on how to accomplish this. Thanks.``` Clarification of Question by bra00424-ga on 16 Oct 2006 07:10 PDT `Also, this is just for fun ... a demonstration for class.` Clarification of Question by bra00424-ga on 16 Oct 2006 12:36 PDT ```I have thought of something...Get a photocell and use color filters and read induced voltage to get idea of different intensities....Should get maximum around yellow light..``` Request for Question Clarification by hedgie-ga on 18 Oct 2006 08:27 PDT ```Hi, bra... Interesting question. The digital camera idea is not bad - and I can find formula to convert RGB values to frequencies. But for a class demostration I would recommed to replicate classical Newton's experiment - and add a bit to get spectrum max. Newton's experiment: http://physics.bemidjistate.edu/archives/Col122502newton01.htm and a diode at green (not yellow) will show max (at noon) --> T= 6000K Do you want few references on that (for \$20) ? Hedgie```
 ```One possible method is as follows: Use a digital camera to take a photograph of the sun. The resulting image file will be millions of pixels, and each pixel will consist of varying amounts of red, green, and blue. You could probably write a simple algorithm to average these values for each pixel and give you a mean effective color. You can convert that color to a wavelength, and voila, you can use that information to find the temperature of the sun. The only problem is that you don't want to completely saturate your image, which would result in a bright white sun. A bright white sun will not really work for this method. So, you'll have to access the manual controls on your camera and underexpose the image as much as possible. A large f-stop value combined with a high shutter speed would do the trick. It sounds a bit tricky, I know, and unless you're used to photography, some of what I just wrote might make no sense. If it's unclear, ask one of your photographer friends on advice in taking the photo.```
 ```The camera trick would not really work, since the rgb values are really outputs of fixed filters. You would essentially get three different weighted averages, and not the complete spectrum. If you need to use a camera for recording you really must separate the different frequencies first, using a prism or something similar. Taking a picture would destroy this information. However I don't think that you need the complete spectrum, just the maximum. As a first approximation I would propose the following: Set up a dark room where you allow a single ray of the sun to enter. Let it pass through a prism, and use a moveable slot to block everything from the output other than a single frequency. Use a photometer at the other end to measure the intensity of the light, and find the location of the maximum. The one (big) problem though is how do you calibrate your measurements, that is how you find the wavelength corresponding to each slot position. One approach would be to use the ends of the visible output, and mark them with the (known) values for the frequencies at the ends of the visible spectrum. I hope this gets you started, although it certainly needs more work to make a practical experiment.```