Atomic Spectra Lab Handout and Report 2014DE_

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George Mason University *

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Astronomy

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Apr 3, 2024

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docx

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Atomic Spectra Lab Handout and Answer Sheet Your Name: Purpose: The purpose of this lab is to examine the atomic spectra from several light sources and understand how spectra can help identify a light’s source. Introduction: Light in all its forms is the primary tool in stellar and galactic astronomy. Through examining various wavelengths of light, ranging from visible light to radio waves to X-rays and everything between, astronomers can learn about the materials that make up stars, galaxies, and the space between them, can figure out distances and masses, temperature and pressure and even rotational speed, age of objects and of the universe. In this lab we will look only at visible light and try to figure out something about the patterns we see from different elements and how those patterns can be clues to other things we want to know. The understanding of spectra is foundational to many of the labs that follow, so it will be important for you to have an opportunity to study them. Procedure: Part I: Fluorescent tube data and Hydrogen spectrum We will provide you spectra from gas discharge lamps, as it is impossible to make those lamps available to students in an online course. Record what you see in the provided spectra and compare the values to the expected lines for hydrogen gas within the limits of the instrument. Repeat with a second spectrum from another tube. Part II: Unknown spectrum The third spectrum will be from an unknown gas, which you need to try to identify. Follow the steps as before, but this time you must compare what you see with spectral charts to identify the element you have been given. Record all values on the answer sheet. Note: Light is usually measured either in nm (nanometers) or Ǻ (Angstroms). A nanometer is 10 -9 m while an Angstrom is 10 -10 m. In this lab, record your values in nanometers. Note that you will see additional numbers (in the range of 1.7-3.4 ) on the top of the scale. You may ignore these numbers. The numbers that correspond to wavelengths are on the bottom of the scale and are in the range of 350-750 nm. Analysis Fluorescent Tube data: You should see a bright green emission line at approximately 546 nm. Record the position of the green line that you see in the first row of the second column in the following table. Do the same for the 436 and 405 nm wavelengths and write down the color that you think they look like in the third column. If you cannot see the 405 nm line write “not detectable”. 1

Fluorescent Light Data Wavelength given on top of spectrometer (nm) Wavelength You Measured (nm) Difference between your wavelength and the given wavelength Line Color 546 545 1nm Green 436 436 0nm Blue 405 not detectable not detectable not detectable Question1 [5 pts]: How will you use the information you just collected when you observe other light sources with the same spectrometer? Think of calibration! We already have information that we've just collected (wavelengths), so when we're observing at other light sources with the same spectrometer, we can compare calibrations to analyze the similarities or differences in color with them. Part II: Measurements of Hydrogen and another known gas 1. Draw lines on the ruler below to show where you viewed lines in the spectrum. On or below the lines you draw, write down the wavelength and the color of the lines you viewed. 2. Use the spectral charts on the internet for example at http://umop.net/spectra/spectrum.php or the spectral charts provided on blackboard and the lines you drew on the ruler to fill out the table below the ruler. 3. Repeat steps using a second gas tube assigned to you 2

Figure1: Various gas discharge tubes similar to those used to get the spectrum 1. Element: Hydrogen or H General color of light emitted by tube: Figure2 : Hydrogen spectrum you measured with your spectrometer Ruler 1 [5 pts.]: Record the positions of the lines shown on the spectrum on the standard spectrum chart. You can insert colored lines by going to the “shape” feature in MS Word. You find it under “insert.” 3

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