Real Spectra Quiz

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Select the letter of the single best answer. Each answer is worth 1 point.

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The above is an attempt to render the visible spectrum on your monitor. Different wavelengths of light (λ, from .380 μm to .750 μm) are seen by the human eye as different colors (V=violet, B=blue, G=green, Y=yellow, O=orange, R=red).

In the previous quiz, plots like the above displayed the amount of light energy as a function of wavelength as a smooth curve. But in fact stellar spectra (and the spectra of essentially all real objects) differ from the ideal blackbody. Much of this quiz will deal with the spectra of real objects as observed in class with the Project STAR spectrometer:

Here is the spectra of the Sun displayed on the wavelength scale of the previous quiz.

If we restrict our plots of sunlight to just the wavelengths of light visible to the human eye, we can line up what you would see with the spectrometer (reversed so things are in a consistent order), an idealized version of the spectrum (from Wiki), and an actual plot of energy flux.

1. The abrupt downward spikes in the spectra, are the result of:
1. Atoms in the Sun's atmosphere eating photons (if they have the "right" wavelength).
2. Photon energy being used to eject electrons from close orbits around the nucleus to more distant orbits.
3. Dark lines in the atmosphere of the Sun.
4. More than one of the above.
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A B C D

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2. A spectra like this is called:
1. Absorption spectra
2. Emission spectra
3. Planck spectra
4. Bright line spectra
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A B C D

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Remarks:

Notice that sunlight (true "white" light) is a mixture of an approximately equal amounts of light at every wavelength detectable by the human eye.

The human eye is a poor color detector (in the sense that actually different light looks the same to us). Unlike a radio receiver which can separately detect any given radio station (e.g., KNSR 88.9 MHz, KSJU 90.1 MHz, etc.), your eye maps the entire visible band into just three "stations": the light detected by the L, M, and S cone cells in your retina (very approximately detecting the colors we call yellow, green, and blue). Using an analogy to sound: imagine an ear to which all the lower third keys on a piano are indistinguishable, the middle third can be distinguished from the lower third, but not each other, and finally a top third. Imagine what a concert would sound like to such an ear, and you can get an idea of how much nuance in light is missed by the human eye! Things that look the same to your eye, can in fact be quite different; the spectrometer can display that difference.

Below find the view of a fluorescent bulb through our spectrometer. The light from a fluorescent bulb may seem a bit odd, but most people will accept it as a substitute for sunlight.

3. Which of the below plots is the best match to the spectra of a fluorescent bulb as seen through our spectrometers as displayed above?

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A B C D

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Parking lot lighting aims for cheap illumination --- not comfortable reading or accurate color presentation. Thus you'll find widely deviant lighting sources outside the home.

The above spectra, as seen through our classroom spectrometer, shows of a low pressure sodium lamp used for outdoor illumination.

4. Which of the below plots is a best match to the spectra displayed above?

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A B C D

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5. A spectra like this is called:
1. Absorption spectra
2. Emission spectra
3. Planck spectra
4. Dark line spectra
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A B C D

```

6. The light produced by this bulb is the result of:
1. Bright lines in the gas enclosed in the bulb.
2. Atoms in the gas spitting out photons whose energy matches that given up by the electron.
3. Diffraction of the photons due to the grating.
4. Excited electrons falling in towards the nucleus.
5. More than one of the above.
6. None of the above.
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A B C D  E F

```

7. Using our spectrometers to view an incandescent (Edison-type) lamp produced the above view. A spectra like this is called:
1. Absorption spectra
2. Emission spectra
3. Continuous spectra
4. Bright line spectra
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A B C D

```

8. GE lighting provides the above comparison of the light from a "soft-white" incandescent bulb and a "Reveal™" bulb. (Reveal is the white line in this plot.) Which of the below spectrometer views shows a reveal bulb? (Note: all of the below are "photoshopped" rather than real spectra.)

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A B C D

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9. The Reveal bulb's spectra is called:
1. Absorption spectra
2. Emission spectra
3. Continuous spectra
4. Bright line spectra
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A B C D E

```

10. When we see the "color" black, it indicates:
1. Black light was emitted.
2. No visible light was emitted
3. A mix of visible wavelengths producing the the perception "black" was emitted.
4. More than one of the above.
5. None of the above.
```
A B C D E

```

Photo Credit: The images through the Project STAR spectrometer were stolen from: Rob Brown