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LAB in Interdisciplinary, Atomic Spectra, Identifying an Unknown, Emission Spectrum, Electromagnetic Spectrum, Emission Spectrum. Last updated January 25, 2019.

Summary

In this lab, the students will make and use a spectroscope to identify the spectra within various types of light bulbs. The students will then develop an improved design for the spectroscope.

Grade Level

Middle or high school

Objectives

By the end of this lesson, students should be able to

  • understand how a spectroscope works to show the unique spectrum of various types of light bulbs.
  • use the spectroscope to match a spectrum to its source.
  • design and construct an improved spectroscope based on the initial experiment

Chemistry Topics

  • Atomic spectra
  • Emission spectrum

Time

Teacher Preparation: 30 minutes

Lesson: Two 60 minutes class periods (one to build the spectroscope and one to use the spectroscope)

Materials

For each student or pair of students

  • Cereal box
  • Ruler
  • Protractor
  • Compact disc
  • Marker
  • Scissors
  • Aluminum foil
  • Tape

For everyone

  • Colored pencils
  • Various types of light bulbs (incandescent, fluorescent, heat lamp, black light, LED and/or gas emission tubes for gaseous element samples)

Safety

  • Always wear safety goggles when using tools in the lab.
  • Never look directly into the sun with the spectroscope.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and unused scraps of box and foil.

Teacher Notes

  • It is best if students work with a partner when making and using the spectroscope.
  • Watch this Build Your Own Spectroscope video to understand the procedure that students will follow.
  • A detailed guide, including pictures, for building the homemade spectroscope has been included for reference.
  • Teachers should build their own spectroscope first, using the included directions so that there is a finished model available for students to reference.
  • The spectroscope works best if the angle cuts on the front and back of the cereal box line up perfectly. Reinforce this to your students, as the spectrum gets distorted if the compact disc is tilted.
  • A clearer spectrum is formed if the light bulbs are surrounded by a box or other materials to block out ambient light sources.
  • A data sheet and answer key has been provided for comparison of known light sources with unknown spectra.
  • Inexpensive spectroscopes can be purchased from a source such as Amazon.
  • For those with access to chemical element gas discharge tubes, the spectroscopes can be used to look at and identify chemical elements.
  • As an extension, the students could look at the spectra of different temperature light bulbs of the same type to see how they compare.

For the Student

Lesson

Problem

How can you identify a specific type of light bulb?

Prelab Questions

  1. When scientists look at stars that are hundreds (or more) light years away, they can determine what chemical elements can be found in that star. How do you think that a scientist can do this even though the star is too far away for a spaceship to reach?
  2. We are now going to watch a short video: NASA Launchpad: Neon Lights – Spectroscopy in Action

At the conclusion of the video, re-answer the above question.

Materials

  • Cereal box
  • Aluminum foil
  • CD
  • Tape
  • Ruler
  • Protractor
  • Scissors
  • Marker
  • Colored pencils
  • Various types of light bulbs

Safety

  • Always wear safety goggles when using tools in the lab.
  • Never look directly into the sun with the spectroscope.
  • Wash your hands thoroughly before leaving the lab.
  • Follow your teacher’s instructions for clean-up and disposal of unused scraps of boxes and foil.

Procedure

  1. Watch this Build Your Own Spectroscope video
  2. The video should serve as an overview for how to make your own spectroscope, and what the final spectroscope should look like.
  3. To begin making your own spectroscope, carefully follow the instructions on the handout “Directions: How to Construct a Homemade Spectroscope.”
  4. Once your Spectroscope has been constructed, point the spectroscope’s slit at the first light bulb, and look through the viewing window.
  5. While looking through the viewing window of the spectroscope, adjust the angle that you are holding the spectroscope and the CD until you see a clear spectrum (rainbow).
  6. Record the type of light bulb in the data table below.
  7. If available, use a phone, iPod, or iPad to take a picture of the spectrum.
  8. Sketch the spectrum in the data table below using colored pencils.
  9. Compare the picture to the spectra on the “Light Bulb Spectra Sheet.” Look for the closest match.
  10. Determine which known spectrum matches the type of light bulb and record its letter on the data table below.
  11. Repeat for the other light bulbs.
Light Bulb Type
 Spectrum Sketch
 Known Spectrum Letter
Data

Analysis

  1. How can you identify a specific type of light bulb if you are unsure of the type of bulb? Write your response in CER (claim, evidence, reasoning) form.

  2. Take your spectroscope outside and look at the sky (DO NOT LOOK DIRECTLY AT THE SUN). You should see a rainbow in your spectroscope much like you would see on a rainy day. What light bulb most closely matches the spectrum of the sun? Explain why it matches better than the other light bulbs.

  3. Some things, such as clothing, look different under different types of light bulbs. Using what you have observed with the spectroscope, why might this be so?

Conclusion

Write a conclusion paragraph that meets the following criteria: answer the initial problem, summarize the experiment, discuss any problems that were encountered, and suggest other experiment ideas.

Design Challenge

  • Choose at least one aspect of the spectroscope to improve.
  • Possible ideas:
    • Make the spectroscope more portable.
    • Reduce the amount of ambient (extra) light that enters the spectroscope.
    • Make the spectrum more sharp and clear (focused).
    • Have the spectroscope use fewer materials.
    • Make it easier to take a picture using the spectroscope.
    • Improve any other problems that you encountered.
  • Build it and test it. Make any additional changes/modifications.
  • Write a set of directions to build the new spectroscope.