Name: Visible spectrum 1 You know by now that different atoms have different configurations of electrons. You also know that electrons generate electromagnetic waves when they oscillate (remember that electromagnetic waves are generated by a moving charged particle). If we were able to make the electrons in the atoms of two different elements oscillate, do you think they will emit the same type of electromagnetic waves? In this lab, we will observe the spectrum generated by different atoms. We will use lamps that work with a particular element in the form of a gas, and spectroscopes to observe their spectrum. We will also use other sources of light. You will use diffracting glasses to see the spectrum generated by different light sources. You will sketch the range of colors observed using the colored pencils (if you brought them), and note the regions where the colors are most bright and most Spectroscope Point the spectroscope to a light source (do not pointed directly to the sun) so the light enters through the slit on the bottom part. You will be able to see the spectrum on the upper side with a bunch of numbers to the left. The numbers in the scale represent 1000 Angstroms. To calibrate the spectroscope, look trough the spectroscope towards a fluorescent lamp and locate the violet and green lines. Write here the approximate wavelength for those lines: Violet: A Green: A The actual wavelength for these lines is: violet at 4360 A and green at 5460 A. Compute the error on your spectroscope here by subtracting the measured value from the actual value for each color and then do an average. Violet: 4360 A - A = Green: 5460 A - A = Average of both errors: 1 This lab was adapted from: http://imagine.gsfc.nasa.gov/docs/teachers/lessons/supernova/supernova_chemistry.html
This is the value that you will need to add to all of the measurements with that particular spectroscope. Procedure Be aware that the diagrams for the spectrographs presented here have units of nanometers (10 A = 1 nm). 1. Incandescent light bulb (white light; regular bulbs) This is a "regular" light bulb. Sketch what you see on the diagram below, marking the wavelengths that define each colored region. Also, mark the limits of your visual range on both ends of the spectrum. Sketch the range of colors observed using the Describe the spectrum that incandescent bulbs produce 2. Candle Redo the same thing: sketch what you see on the diagram below, marking the wavelengths that define each colored region. Also, mark the limits of your visual range on both ends of the spectrum. Sketch the range of colors observed using the
Compare to the incandescent bulb spectrum 3. Hydrogen gas tube 4. Helium gas tube 5. Neon gas tube
6. Mercury gas tube 7. Nitrogen gas tube 8. "Plant Grow" light bulb This is an incandescent bulb that is supposed to provide more light in the wavelengths that plants can use than normal light bulbs. On your data sheet, sketch what you see, marking the wavelengths that define each colored region. Also, mark the limits of your visual range on both ends of the spectrum. Sketch the range of any colors observed using the colored pencils, and note the regions where the colors are most bright and most
9. Compact Fluorescent light fixture Because fluorescent lights use considerably less electricity than incandescent bulbs, these light fixtures have been invented so that fluorescent lights can be screwed into regular light bulb sockets. They are manufactured in a different way from regular fluorescent tubes. Measure and draw the wavelength of any line spectra that appear on the blank spectrum on your data sheet. Sketch the range of any colors observed using the colored pencils, and note the regions where the colors are most bright and most 10. Chemical Light Sticks These light sticks work by a chemical reaction which releases light energy instead of heat, sound, or electricity as other reactions may do. The reaction is very similar to the one that occurs in the tails of fireflies! On your data sheet, sketch what you see, marking the wavelengths that define each colored region. Also, mark the limits of your visual range on both ends of the spectrum. Sketch the range of any colors observed using the colored pencils, and note the regions where the colors are most bright and most 11. Fluorescent light source Turn your spectrometer slit toward a standard fluorescent light tube. This type of lighting is very common in schools and offices because it uses much less electricity than traditional incandescent light bulbs. Measure and draw the wavelength of any line spectra that appear on the blank spectrum on your data
sheet. Sketch the range of any colors observed using the colored pencils, and note the regions where the colors are most bright and most Complete the following questions. Questions 1. Summarize your comparison of the different spectra. 2. Compare the results of the various gas tube spectra with the spectrum observed using the standard fluorescent light tube. What gas do you think is used in fluorescent light tubes? 3. Was there any difference between the spectra of the standard fluorescent light tube and the compact fluorescent light fixture? Why do you think this is so? 4. How can we use this information in Astronomy?
5. Compare the results of the incandescent light bulb with the spectra of the fluorescent light tube and the compact fluorescent light fixture. Why would the fluorescent lights be considered as more "energy efficient"? Could there be a disadvantage to this? 6. What else would you like to know about atomic spectra?