Activity 2: Spectroscopy

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Concepts
Learning Objectives
Set-Up
How To Demonstrate
Questions To Ask
Sample Dialogue
What's Next?


Concepts
  • In order to measure the carbon in our atmosphere, we can measure the specific color of light absorbed by carbon.
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Learning Objectives
  • The visitor will use spectrum glasses and a prism to see that light is made of different colors. Using an emission spectrum tube, the visitors will see that different materials, such as carbon, emit and absorb specific colors.
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Set-Up
  1. Plug in the emission spectrum tubes, and put the tubes in the holders.
  2. Take out the spectrum glasses.

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How To Demonstrate
  • Attract visitors by asking them questions like, “Want to wear these awesome glasses?” or “Want to see something cool?”
  • Give the visitor a pair of spectrum glasses and ask them what they see. Let them know that white light is made of different colors. Each color is a different wavelength.
  • Ask the visitors if they think that what is in the air could affect the wavelengths that we see. Let them know that the air is made up of different elements, and different elements emit and absorb different wavelengths of light.
  • Take out the emission spectrum tubes. Explain that each tube contains a gas. The gases are made up of one element or a combination of elements, like the air. The device sends a current through the gas, which excites it. When the gas gets excited, it emits a wavelength—a color unique to that element.
  • Show the visitors how to insert the tubes, and have them insert different tubes to see what wavelength of light different gases emit.
  • Let the visitors know that the atmosphere contains mostly nitrogen, some oxygen, and some other gases such as argon and carbon. Encourage the visitors to compare the different wavelengths emitted by these gases to the wavelength emitted by air.
  • Let the visitors know that the color they are seeing when the element is excited is the same color that is absorbed when light shines through that element. When light shines through the air, specific colors are being absorbed by the elements in the air.
  • Take out the spectrum glasses and/or prism again. Let visitors know that with similar but more advanced equipment, we can see which specific wavelengths are being absorbed by different elements. Using this information, we can determine which elements are in the air and how much of them there are.
  • Let the visitors know that using the wavelengths of light absorbed by carbon, we can determine how much carbon is in the air.
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Questions To Ask
  • What color is sunlight?
  • Have you ever seen a rainbow?
  • Do you know what an element is?
  • Can we see gas?
  • How can we measure how much of an element is in the air?
  • What does absorption mean? Emission?
  • Do you know what a wavelength is?
  • How many different colors do you think there are?
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Sample Dialogue

Key:
  • P    Presenter
  • G    Guest
  • Bold italics indicate action.
  • Italics indicate a note to the presenter.
  •    □ indicates a cue


P   Hi there! Want to see something cool?
G   Sure.
P   Put on these glasses and look at the light. What do you see?
G   Rainbows!
P   Neat! Why do you think you see rainbows?
G   There are rainbows in the glasses?
P   Interesting. Let's experiment. Take the glasses off, and try shining this flashlight through this prism. What do you see?
G   Rainbows.
P   Right. This prism is just glass. Where do you think the rainbows are coming from?
G   Maybe the light.
P   Awesome. What color is the light without the prism or glasses?
G   Yellowish.
P   Okay. What color is the Sun?
G   Yellowish.
P   Yeah. Sometimes the Sun can look like different colors. For instance, what color is the Sun when the Sun is setting?
G   Red.
P   Right. The Sun might look different colors at different times depending on how it's shining through the sky. In space, there isn't a sky. There's no atmosphere. What color do you think the Sun is in space?
G   Yellow?
P   I used to think that too, but pictures show that the Sun is white. Most of the light we see from light bulbs is white as well. Prisms can separate white light into the colors that make light and show us all the colors in light. Have you ever seen a rainbow in the sky?
G   Yes.
P   What do you think is happening when there is a rainbow in the sky?
G   Something about the rain.
P   Right. Rain can act like a prism, separating the white light from the Sun into all its different colors. Do you think anything else in the air could affect the light we see?
G   Sure.
P   Right. Let's think about what's in the air. Do you know the name of the gas we breathe?
G   Oxygen.
P   Awesome. And what do we breathe out?
G   I don't know.
P   We breathe out a gas called carbon dioxide. Can you say that?
G   Carbon dioxide.
P   Right. Carbon and oxygen are elements. Different elements can absorb different colors of light. And when you put an electric charge through those elements, they can also give off those different colors. Would you like to try it?
G   Sure.
P   Fabulous. I have here a little machine that will put an electric charge through an element. This here is a spectrum tube. What do you see?
G   A clear part and some black plastic.
P   Yep. The clear part is a glass tube that holds the element. Can you read what element this is?
G   Oxygen.
P   Awesome. Let's see what color of light oxygen gives off if we charge it. What color is that?
G   Blue.
P   Cool. Do you think different elements give off different colors?
G   Yeah.
P   Let's check out what other elements give off. What's this one?
G   Nitrogen.
P   Where have you heard of nitrogen before?
G   I think it might be like a liquid or something.
P   Yeah, at the science center we have liquid nitrogen, which you can't find naturally on Earth. To make it a liquid we have to make it really, really cold, because usually it's a gas we find in our atmosphere. What color is it?
G   Purplish.
P   Great. Now let's try carbon dioxide.
G   Blue!
P   Neat. Now, what color is the Sun again?
G   White.
P   Definitely. What elements do you think are in the Sun?
G   Um. Maybe . . . helium and argon?
P   Let's check those elements.
G   Orange and green.
P   Great. The Sun isn't orange and green, though. Do you remember what colors make white light?
G   A rainbow.
P   Right. So the Sun has all the colors together in order to make white light. So what elements do you think it has?
G   All of them?
P   Absolutely. Looking at what color of light an object gives off can tell us something about the elements in that object. Do you think we could tell what elements are in the sky by looking at the light they give off?
G   Yes.
P   That makes sense, right? But remember we had to put electricity through these gases to make them shine. The gases in the atmosphere don't shine. Instead, they react to light from the Sun. How do you think they react?
G   They separate the light into colors.
P   Rain can do that, true. And elements in the atmosphere do that to some extent--they scatter blue light more than the other colors, which is why the sky looks blue. But each specific element absorbs a very specific color of light. What color do you think carbon dioxide absorbs?
G   I have no idea.
P   Do you remember what color it emits?
G   Blue.
P   Right. When we put electricity in it, it emits blue. When you put sunlight in it, it sucks up that exact same color! How do you think we could use this to see if carbon dioxide is in our atmosphere?
G   You could see what color it sucks up.
P   Awesome! By looking at what color of light is absorbed by our atmosphere, we can tell what elements are in our atmosphere. Thanks for looking at different colored lights with me!
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