Atomic Spectra Lab

Atomic Spectra Lab

Purpose: 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 element 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 to have a hands-on opportunity to study them.

Procedure:

Part I: Diffusion grating glasses

Begin by using the diffraction glasses to look at a variety of sources and record your observations. You should record what the light source is, and as much detail as possible about what you see. Try moving closer and farther from the source and seeing if there are changes. Also try tilting your head to see what happens. On your answer sheet record what you observe so that someone else could visualize it.

Part II: Spectrometer Calibration

The spectrometer you will use to look at light from various emission tubes has a scale inside that can be moved a small amount. Because you need to record the wavelengths of the spectral lines you see as accurately as possible within the limits of the equipment it is necessary to calibrate the scale. You need to know how much it is “off” in order to adjust the value you read during the lab and to do that you need a reference of known wavelength.

Notice the list of spectral lines and their wavelength values on the side of the spectrometer. When you aim the spectrometer at the overhead lights you should see some of these lines, particularly the green Mercury line at 546 nanometers. On your answer sheet record the actual scale reading for this line and others as seen on your spectrometer.

Part III: Hydrogen spectrum

Turn on the high voltage power source with a hydrogen tube inserted and examine the spectrum following the instructions on the answer sheet. Record what you see and compare the values to the expected lines for hydrogen gas within the limits of the instrument. Repeat with a second tube assigned by the instructor

Part IV: Unknown spectrum

You instructor will give you a third tube, an unknown 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.