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Nature_of_Light.pdf - Spectra Student Guide Introduction:...

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1 of11Spectra Student GuideIntroduction:In this lab, you’ll use a high-quality spectrometer, made by Project STAR, to examinethe spectra of a variety of light sources. The main goals are to practice accuratelyobserving and recording the appearance of a spectrum and to think about the differenttypes of spectra and the characteristics of the objects that create them.Background material:The spectrum of a light source shows how the light intensity varies with thewavelength of light. Basically, a spectrum records how much light is produced at eachcolor. There are three main categories of the spectrum, which are produced in thefollowing three situations:1.A hot opaque body, such as a dense gas or solid, produces a continuous spectrum– a complete rainbow of colors. Theintensity varies smoothly with wavelength.2.A hot, low-density gas produces anemission line spectrum – a series of brightspectral lines against a dark background.Light is only emitted at specificwavelengths.3.A cool, low-density gas in front of a hotopaque body produces an absorption linespectrum - similar to a continuousspectrum, except with dark lines (dips inintensity) at specific wavelengths.Emission and absorption lines have a characteristic pattern that is determined by thecomposition of the gas involved. For a given type of gas, the bright lines in an emissionspectrum, where the hot gas emits light, occur at exactly the same wavelengths as thedark lines in the absorption spectrum, where the cool gas absorbs some of thecontinuous spectrum’s light.By measuring the spectrum of stars and nebula, and comparing them to spectraobserved in labs on Earth, astronomers are able to learn about the temperature andcomposition of distant objects.Review the background material on light and spectra:
2 of11Using the Spectrometer:Figure 1: The STAR Spectrometer. Note the locations of the eye hole, the calibratedscale that you look at through the eye hole and the position of the source with respectto the spectrometer. This is explained in detail below.Hold the spectrometer so that you can look through the grating in the narrow end. Youshould be able to see two rows of calibration marks and numbers. Pay attention to thelower row, which gives the wavelength (in nanometers, or nm) of the light in thespectra above it.

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Term
Winter
Professor
bennert
Tags
Light, Incandescent light bulb, Fluorescent lamp, spectra of a variety of light sources

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