Atomic Spectra Lab Handout and Report 2014DE_.docx

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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Ruler 2 [ 5 pts.]: Record the positions of the lines that you measured with your spectrometer Lines on spectral chart (Ruler 1) but not on Ruler 2. Lines not on spectral chart (Ruler 2) but on Ruler 1. Wavelength Color Wavelength Color 660 Red 655 Red 495 Sky Blue 485 Sky Blue 470 Purple 435 Dark Blue 420 Dark Blue Table 1 [5 pts.] Element assigned: Argon or Ar General color of light emitted by tube: Figure 3: Argon spectrum you measured with your spectrometer 4

Ruler 1 [5 pts.]: Record the positions of the lines shown on the spectrum on the spectrum chart. (Use the same URL as for hydrogen) Ruler 2 [5 pts.]: Record the positions of the lines that you measured with your spectrometer Lines on spectral chart (Ruler 1) but not on Ruler 2. Lines not on spectral chart (Ruler 2) but on Ruler 1. Wavelength Color Wavelength Color 590 Red 655 Red 520 Green 559 Red 450 Dark Blue 520 Green 487 Sky Blue 455 Dark Blue Table 2 [5 pts.] Part III: Unknown element Record all the lines possible and use the spectral charts to try to identify the element. Remember to use the calibration information from Part I of the lab to increase the accuracy of your observations. 5

Figure 4: Unknown gas discharge tube General color of light emitted by tube: Figure 5: Measured spectrum of the unknown element Ruler 1 [10 pts.]: Record the positions of the lines you see on the spectrometer here. 6

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In the space below list possible elements that might match the lines you have recorded (you should find at least one, but there may be several possibilities depending on your unknown). 1. Use the following table to compare wavelengths for your unknown and the potential elements you think it could be. Line Color Recorded wavelength of unknown element Corresponding wavelength for Possible Element #1 Corresponding wavelength for Possible element # 2 Corresponding wavelength for Possible element # 3 Red 645 655 (Neon) 650 650 Red 605 N/A 605 N/A Yellow 585 577 587 576 Green 550 520 557 555 Dark Blue 450 N/A 450 N/A Dark Blue 425 450 430 435 Table 3 [10pts.] 2. [5 pts.] Based on data in the table, explain what the most likely possibility is for your element. Hint: take a look at the color of the tube and compare to those pictures in the earlier part of the report. The most likely possibility element is Krypton. 3. [5 pts.] Short of asking the instructor, how could you test whether your guess is correct? This is because, based on the data, the recorded wavelength matches with the wavelength of Krypton. Moreover, the color of the tube also matches the color with Krypton. Question 1 [10 pts.]: Would you expect different elements such as hydrogen, helium, oxygen, and nitrogen to have emission lines that are the same or different from each other? Do you think all elements should have at least some lines in common, or do you expect them to be different for each element? In a paragraph explain your reasoning. My inference is that these elements will have different emission lines. I learned from ASTR 114 that each element has its own emission line, which is distinguishable because it exists in its own form, just like human fingerprints. For example, in terms of emission lines, Helium has more electrons than hydrogen, so I think all of these elements will have different emission lines. Question 2 [5 pts.]: For any of the elements, were there any lines missing from your ruler (Ruler 2) that were on the spectrum chart? If yes, suggest at least two reasons why. 7

Yes, there was a missing line. This is because this is a part that we can't see except for the visible light range of 400 nm to 700 nm. Also, due to misalignment, it may be missing due to the measurer's mistake. Question 3 [10 pts.]: Based on your results in the table for the fluorescent lights, how accurate (in nanometers) the values are that you wrote down for the locations of the spectral lines on your rulers for the three elements? How precise (in nanometers) do you think your values are? Explain your reasoning below. The value may not be accurate because it may be due to an error in the ruler or my fault for reading the value incorrectly. Also, I tried to infer the most accurate value, but it may not be accurate because each element has a different ruler ( not the same mark ). However, I would like to say that the error is within 10 nanometers because I have checked several times to infer the most accurate value. Question 4 [5pts.]: Why do you think we have so many telescopes on satellites that orbit Earth given that they are more expensive than ground-based telescope? This is because telescopes on satellites orbiting Earth provide highly accurate and clear images compared to ground-based telescopes, so there are many telescopes on satellites. In addition, ground-based telescopes are affected by celestial events, such as climate and temperature, but those in orbit are relatively less affected. Thus, it is important for us to check the exact information, so many telescopes are installed on satellites orbiting Earth. Question 5 [5 pts.]: If we did not have a spectral chart for water, could we just combine the spectral charts for Hydrogen and Oxygen? I do not think because the water has unique its own atom which is the combination of two hydrogen and oxygen. 8