PERFORMANCE ASSIGNMENT Lab 16

Elemental Analysis

With a Bright-Line Spectrum

BACKGROUND INFORMATION:

Just as sound comes in different notes, light comes in different colors. The colors we see are only a very small part of what is called the electromagnetic spectrum. The electromagnetic spectrum includes wavelengths above and below what we can see as visible light. Some examples include; gamma rays, X-rays, ultraviolet, infrared, microwaves, and a variety of radio waves. The sun gives off all these and more, streaming into space at the same speed for all: the Speed of Light. We can detect and measure parts of this spectrum, using a variety of instruments, even though we can not see them. Some of the wavelengths are able to penetrate the atmosphere while others can not. Because information contained in the wavelengths that can not penetrate the atmosphere are important, we send satellites into space to record them.

Purpose:

The study of the electromagnetic spectrum is of utmost importance in revealing the secrets hidden in the vastness of space. One of the few ways that astronomers have to unlock these secrets, lie in the electromagnetic radiations sent to us from distant suns. In the following activities you will see how the spectrum is used to study our universe as well as more distant galaxies.

MATERIALS:

spectroscope or diffraction grating
Spectral chart showing absorption lines.
3 thermometers
light source (sun)

Part 1

Set up thermometers so than one is in the blue, one in the red and one in the middle. Allow thermometers to adjust to the temperature for about 5 minutes before creating and exposing them to the spectrum. After the thermometers have adjusted, use the prism to create a spectrum. Place thermometers at several points in the spectrum: one in the violet range, one in the center, and one just barely beyond the red end. Leave the thermometers in the spectrum for at least 5 minutes, moving carefully as the sunlight moves the spectrum. Temperature changes may be very small, so read them carefully.

QUESTIONS:

What were the final readings on the thermometers? Should they all be the same? Why or why not?
Why might there be an increase at one end of the spectrum as opposed to the other?
What does this tell us about the "invisible" red end of the spectrum?

Part 2

In this activity you will see how scientists can determine what elements are present on stars that are hundreds of light years away. Electromagnetic waves given off by stars contain information as to their make-up (elements present) in what are known as absorption spectral lines. These lines look like the "bar code" lines you see on items from stores. Each bar code tells the supermarket scanner what the item is and how much it costs. Spectral lines, from stars, tell scientists what the item (element) is, but not how much it costs yet! Look at the sample spectrums and record the bright line spectrum for each. Then look at the unknown spectrums and try to identify which element it is.

SAMPLE 1: ________________