Download Astr. 170B1 Due Feb. 5 Professor Rieke and TA Melissa Halford

Astr. 170B1 Due Feb. 5 Professor Rieke and TA Melissa Halford Homework on spectroscopy, colors, and light. This portion of the homework is worth 30 points. Correct responses shown in boldface. 1. Is the spectrum below a. an absorption line one b. a continuum c. an emission line one d. Doppler shifted e. unresolved 2. If a photon of energy E has a wavelength of 0.6 microns, what energy photon will have a wavelength of 0.3 microns? a. 2 times E b. Half of E c. 4 times E d. ¼ of E e. the energy cannot be determined accurately 3. The figure on the left illustrates electronic transitions from 3 higher levels to a lower one (52, 42, or 3 2) in the hydrogen atom. Which transition produces a photon with the highest energy? a. 5 ‐> 2 b. 4 ‐> 2 c.3 ‐> 2 4. Which transition produces a photon in the reddest portion of the spectrum? a. 5 ‐> 2 b. 4 ‐> 2 c. 3 ‐> 2 An energy level diagram showing the 3 hydrogen transitions which give the strongest lines in the visible spectrum. 5. Considering the effect of the cloud on the spectrum of the star, what type of spectrum does the observer see in the figure on the right? a. absorption b. emission c. continuous © M. Rieke
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6. How are the electrons in the atoms in the hydrogen cloud in the figure above behaving? a. They are jumping from a lower to a higher level b. they are jumping from higher to lower c. They are leaving the cloud d. We cannot know how they are moving e. They are jumping from a lower to a higher level and then eventually falling back to the lower level 7. The young, hot star in picture to the left heats up the gas in the cloud. Assume that the observer can only see radiation emitted by the hydrogen cloud and cannot see the star. What type of spectrum (emission, continuous , or absorption) does the observer see? a. absorption b. emission c. continuous 8. How are the electrons in the atoms in the hydrogen cloud in this figure behaving? a. They are jumping from a lower to a higher level b. they are jumping from higher to lower c. They are leaving the cloud d. we cannot know how they are moving e. They are jumping from a lower to a higher level and then eventually falling back to the lower level 9. Look at the spectrum of the Sun below. What type of spectrum (continuous, emission line or absorption line spectrum) does the Sun produce? a. absorption b. emission c. continuous The next few problems will be much easier if you review how to use scientific notation (see http://janus.astro.umd.edu/astro/scinote/ for more practice) 10. Hydrogen has a spectral line that is observed at a wavelength of 656 nm (656x10‐9 meters). Recalling that the speed of light is c = 3x108 meters/sec and the relationship between wavelength and frequency, frequency = c/wavelength, what is the frequency of the photons observed as this spectral line? a. 4.6x1014 Hz b. 2.2x10‐15 Hz c. 100 MHz d. 4.6 Hz e. Cannot be computed © M. Rieke
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11. The photons producing the hydrogen line in question 10 also have energy. Review the relationship between energy and frequency given in the lectures, energy = h times frequency. Use h=Planck’s constant = 6.6x10‐34 Joules/Hz to compute the photon’s energy which is ___________ Joules. d. 24x1019 e. 7x1047 a. 3 b. 3.0x10‐19 c. 24 12. If you observed the hydrogen line discussed in questions 10 and 11, what color would it have? a. purple b. green c. white d. all the colors of the rainbow e. red A. B. Examine the two spectra above. Go to http://spiff.rit.edu/classes/phys301/lectures/spectra/spec_rev_orientation.gif or http://www.amateurspectroscopy.com/color‐spectra‐of‐chemical‐elements.htm and compare the spectra shown there with these spectra. 13. The spectrum labeled A. above is produced by which element? a. lithium b. hydrogen c. helium d. carbon e. no way to tell 14. The spectrum labeled B. above is produced by which element? e. no way to tell a. lithium b. hydrogen c. helium d. carbon © M. Rieke
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A. B. C. D. 15. The spectra of four stars are shown above. Which star’s spectrum is dominated by spectral lines from hydrogen? A. B. C. D. E. none are 16. The spectrum plotted above is from a real star, Vega. The spectrum is also shown in color as it might appear to your eye. What element’s absorption lines are prominent in Vega’s spectrum, particularly in the blue? a. lithium b. hydrogen c. helium d. carbon e. no way to tell © M. Rieke
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The plot at the right shows a magnified section of the Vega spectrum in black. You may assume that Vega is not moving. The red plot is part of the spectrum from another star very similar to Vega except for its Doppler shift. The numbers show the location of the spectral line. Use c=300,000 km/sec 17. In what direction is the star 410.2165 410.4216
producing the red spectrum moving? a. Toward us b. Away from us c. Cannot be figured out from this plot 18. How fast is the star producing the red spectrum moving? a. 300,000 km/sec b. 150 km/sec c. 15000 km/sec d. 0.205 km/sec e. 61,500 km/sec 19. The graph below shows the output of a black body at a temperature of 5000K, plotted against the wavelength. The peak is at 0.58 microns. How would the output against wavelength change if the temperature were 2500K? a. it would stay the same b. it would get fainter but otherwise stay the same c. the shape of the curve of output against wavelength would change d. the peak of the output would appear at 1.16 microns e. the peak of the output would appear at 0.29 microns 1.4
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20. In the situation described in problem 19, with the temperature going down by a factor of two, how will the total output over the entire range of wavelengths (the luminosity) change? a. stay the same b. get 2 times smaller c. get 4 times smaller d. get 8 times smaller e. get 16 times smaller 21. At which temperature would the peak of the output be in the far infrared, near 100 microns (100x103 nanometers)? (Note that the equation in the lecture notes uses nanometers as the unit for wavelengths and degrees K for temperatures. 1 micron = 1000 nanometers.) a. 250K b. near absolute zero c. 29K d. ‐57C e. None of the above For the following questions, you will need to refer to the spectra you measured in the class. 22. Spectrum number 1 is a. helium b. mercury c. neon d. none of those 23. Spectrum number 2 is a. helium b. mercury c. neon d. none of those 24. Spectrum number 3 is a. helium b. mercury c. neon d. none of those 25. Spectrum number 4 is a. helium b. mercury c. neon d. none of those 26. Spectrum number 5 is a. helium b. mercury c. neon d. none of those 27. The mystery gas is a. argon b. helium c. hydrogen d. xenon e. none of these 28. The fluorescent lights emit a. a continuous spectrum b. a line spectrum c. a spectrum with lines and continuum together © M. Rieke
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29. The incandescent light (light bulb) emits a. a continuous spectrum b. a line spectrum c. a spectrum with lines and continuum together 30. What gas is in the fluorescent lights? a. helium b. mercury c. neon d. hydrogen e. argon ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ The forms below are for you to draw in the spectra you observe in class and to turn in (paper copies). In addition to sketching in the spectral lines you observe, you should also indicate what colors are seen along the spectra. We have provided extra ones in case you need them. You should have six drawings; label the ones you want graded in the margin, and be sure to put your name on the forms you turn in (and staple them together): This portion of the homework is worth 10 points. 1. helium lamp 2. neon lamp 3. mercury lamp 4. mystery lamp 5. fluorescent room light 6. incandescent light (light bulb) Be warned: We have two brands of spectrograph (old and new). For the old ones, the wavelength scale is to the left of the slit and the wavelengths run from large to small, left to right (as shown below); for the new ones, the wavelength scale is to the right of the slit and the wavelengths run from small to large, left to right. If you are "lucky" enough to get a new spectrograph, be careful that you plot the lines in the right places!
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Mystery gas = hydrogen
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