3.8: Applications of Spectroscopy

3.8.1 Types of Spectra

Model

The model below shows the three types of spectra

Hot star, cool gas cloud, and resulting continuous, emission, and absorption spectra.

1. What colors of light are given off by the star?
2. Do all of those colors pass through the cool cloud? If not, what happens to those colors?
3. When a hot object radiates light due to its temperature, what type of spectrum does it give off?
4. When light passes through a cold gas, what type of spectrum do you see if you are looking at the light that passes through the gas from the source?
5. When light passes through a cold gas, what type of spectrum do you see if you are looking at the light emitted from that gas, not the original source?
6. Use the model images in class to match the spectrum to the Energy Output Plot on the next page.

3.8.2 Blackbody Radiation Plots

Model

The simulation below shows the amount of light each section (power) for each wavelength of light. The peak of the red curve shows which wavelength is emitted the most. Explore the simulation below:

• Change the temperature to see how the red curve changes up/down and left/right
• Zoom in or out as needed to see the data
• Examine the star color, which is right next to the B, G, R circles above the graph

Simulation Source: https://phet.colorado.edu/sims/html/blackbody-spectrum/latest/blackbody-spectrum_all.html

1. When the temperature increases, does the curve get taller/shorter? Does it get wider/narrower?
2. When the temperature increases, does the peak of the curve move left or right? Is this towards a higher
   or lower wavelength?
3. Are all visible wavelengths emitted at any temperature? You might need to zoom in to check if some are nonzero.
4. Is this a continuous spectrum, emission spectrum, or absorption spectrum? Explain how you know.
5. If you saw two curves, how could you tell which one represented a hotter star? Be specific.

1.3 Radiation Plot with Absorption and Emission Spectra

Model

Go to the Spectrum Constructor fromFoothill AstroSims: https://foothillastrosims.github.io/...m-Constructor/

• Select Thermal and adjust the temperature. This is a zoomed in (flatter) plot of what you explored in the PhET Radiation Plot simulator
• Reset the temperature 5800K. This is the surface temperature of our sun
• Select Hydrogen on the absorption spectra panel.
• Explore other elements one at a time in the absorption spectra panel

1. How does the Diffraction Grating image compare to the Spectrometer View graph?
2. Choose an element and compare its Emission Spectrum to its Absorption Spectrum (only have one checked at a time). Describe similarities and differences between the two spectra
3. Four different reference spectra are shown for different elements (a–d). On the right, there is a blackbody radiation plot.
   1. Which spectrum do the lines on the radiation plot match? Explain your thinking.
   2. Is the plot an emission or absorpotion plot? Explain your reasoning.
   3. How would the energy output look different for the opposite (absorption or emission) of light at those wavelengths? Explain your reasoning and draw it on the blank template below.

Four reference spectra and a blackbody radiation plot with absorption features.

Image Credit: Center for Astronomy Education (CAE) (https://www.as.arizona.edu/cae/materials_resources/)