Astronomy 1002
Homework #5

 



 

1. The only difference between visible light and radio waves is that

 

    1. radio waves have longer wavelengths than visible light.
    2. radio waves have shorter wavelengths than visible light.
    3. visible light is electromagnetic radiation, but radio waves are not.
    4. radio waves can be heard, whereas visible light cannot be heard.
    5. there is no difference between the two.
 


 

2. Two sets of waves can combine with each other to produce a resultant wave. This phenomenon is called?

 

    1. refraction.
    2. diffraction.
    3. interference.
    4. defraction.
    5. polarization.
 


 

3. What do all kinds of electomagnetic energy have in common?

 

A. They all have the same frequency.
  1. all have the same wavelength.
  2. all are observed in the same way.
  3. all have the same speed in a vacuum.
  4. are all usually measured in angstroms.
 


 

4. The tendency of light to bend at the edge of an opening is called?

 

  1. polarization.
  2. dispersion.
  3. refraction.
  4. reflection.
  5. diffraction.
 


 

5. Which of the following effects demonstrates the wave-nature rather than the ray-nature of light?

  1. diffraction
  2. interference
  3. reflection
  4. refraction
  5. both A and B
 


 

6. Which of the following lists the various forms of radiation in order of -longest- to -shortest- wavelength?

 

  1. shortwave, microwave, visible,infrared
  2. visible, ultraviolet, X-rays, gamma rays
  3. ultraviolet, gamma rays, infrared, shortwave
  4. X-rays, microwaves, ultraviolet, infrared
  5. microwaves, infrared, shortwave, X-rays
 


 

7. The Moon is about 400,000 km from Earth. About how long would it take a radar signal from Earth to reach the Moon?

 

  1. a fraction of a second
  2. 1.3 seconds
  3. 2.6 seconds
  4. about 1 minute
  5. It would be virtually instantaneous.
 


 

8. The _____ the frequency of light, the ______are the photons of which it is composed.

 

  1. higher, more energetic
  2. higher, less energetic
  3. lower, more energetic
  4. high, faster
  5. lower, bluer
 


 

9. When an electron jumps from an excited state to the ground state in an atom,

 

  1. the atom is said to be ionized.
  2. the electron gains energy.
  3. a photon is emitted.
  4. a photon is absorbed.
  5. the process is called recombination.
 


 

  1. When an atom changes from a lower to a higher energy level, the process is called
 
  1. neutralization.
  2. ionization.
  3. perturbation.
  4. excitation.
  5. recombination.
 


 

11. How much more energy does each unit area of a 25,000 K star radiate than a 5,000 K star?

 

  1. 5 times
  2. 25 times
  3. 125 times
  4. 625 times
  5. The answer depends on the size of the star, which is not given.
 


 

12. Suppose you have a detector that captures 1000 photons with a wavelength of 100 Angstroms each. How many photons would you need to collect in order to have the same total amount of energy if the photons had a wavelength of 20 Angstroms?

 

  1. 5
  2. 10
  3. 50
  4. 200
  5. 1,000
 


 

13. What can you infer about a gas from which you observe bright emission lines?

 

  1. It is hot, with a temperature in excess of 10,000 K.
  2. It has a low density.
  3. It is a dense gas.
  4. It has a low temperature.
  5. both A and C
 


 

14. Different chemical elements exhibit different spectral lines because the atomic energy levels are established by?

 

  1. spectral lines are not unique to the atom.
  2. the neutron-electron interaction is unique for each atom.
  3. each type of photon emitted by the atom is unique.
  4. different nuclear charges produce different sets of electron orbits.
  5. the mass of each atom.
 


 

15. In an atom that absorbs a photon,

 

  1. an electron moves to a larger orbit.
  2. an electron moves to a higher energy level.
  3. the atom may become ionized.
  4. it is likely to spontaneously change its energy state again soon.
  5. all of the above.
 


 

  1. What gas do we see when we examine the spectrum of an incandescent light bulb?
 
  1. neon
  2. We see the continuous spectrum from the hot filament, not the spectral features of a gas.
  3. hydrogen
  4. mercury
  5. sodium
 


 

17. Suppose we observe a star that has a ring of low-density gas around its equator. The star is so distant that it is just a point of light, so we cannot see the ring directly. Suppose that this low density gas is at a higher temperature than the surface of the star. What will we see, in addition to a continuous spectrum with absorption lines from the star's atmosphere, when we examine the spectrum from this object?

 

  1. absorption lines from the ring
  2. emission lines from the ring
  3. a continuous spectrum from the ring
  4. both A and B
  5. both B and C
 


 

18. Wien's Law

 

  1. describes the changing intensity of an object as its temperature changes.
  2. relates the temperature of a radiating object to the wavelength at which it will emit the most energy.
  3. gives a mathematical relationship between the color of an object and its reflective properties.
  4. says that rarefied gases will emit energy only at certain discrete wavelengths.
  5. is a more recent and more refined version of Kirchhoff's law.
 


 

19. When a cool gas cloud intervenes between an observer and a source of light that emits light of all wavelengths, the observer would see

 

  1. an emission spectrum characteristic of the gas cloud.
  2. a magnified image of the gas cloud.
  3. an absorption spectrum characteristic of the gas cloud.
  4. no change in the spectrum of the source of light.
  5. a complete continuous spectrum.
 


 

20. Choose the true statement concerning the seats in a room ( temperature = 300 K )

  1. The seats are radiating electromagnetic energy at wavelengths around 100,000 Angstroms; this explains their color.
  2. The seats are radiating electromagnetic energy primarily at visual wavelengths, and this explains their color.
  3. The seats are radiating electromagnetic energy at wavelengths around 100,000 Angstroms, but their color is explained by the way in which they reflect light.
  4. The seats are radiating electromagnetic energy primarily at visual wavelengths, but their color is determined by how they reflect light.
  5. None of the above statements is true.
 


 

21. If a star is surrounded by a ring of low density gas that is at a lower temperature than the surface of the star, the observed spectrum of the star plus ring will exhibit (in addition to the star's continuous and absorption spectrum)

 

  1. a continuous spectrum from the ring.
  2. absorption lines from the ring.
  3. emission lines from the ring.
  4. both A and B.
  5. both B and C.
 


 

22. Ionization means that an atom

 

  1. jumps into the ground state.
  2. jumps into an excited state.
  3. loses an electron.
  4. absorbs a photon.
  5. becomes a molecule.
 


 

  1. A photon of wavelength 912 Angstroms can ionize a H atom from the ground state. Then a photon with a wavelength of 913 Angstroms
 
  1. can ionize a H atom from any energy level
  2. can ionize a H atom from its ground state, but not from any other level.
  3. cannot ionize the H atom in its ground state but can ionize it from all the excited states.
  4. can ionize a H atom if it is bound up in a molecule.
  5. cannot ever ionize a H atom.
 


 

24. In the figure above, the energy curves of four bodies emitting a continuous spectrum are exhibited. The energy given off at every wavelength is plotted against the wavelength. Which of the objects is the coolest?

  1. A
  2. B
  3. C
  4. D
  5. E
 


 

25. What fraction of the number of atoms in the universe is hydrogen?

  1. <50%
  2. 70%
  3. 80%
  4. 90%
  5. >90%
 


 

26. Who discovered that most of the universe is hydrogen?

  1. Isaac Newton
  2. Galileo Galilei
  3. Edwin Hubble
  4. Cecilia Payne-Gaposchkin
  5. Annie Jump Cannon
 


 

27. A man accused of running a red light claims that what really happened was that he was going so fast that it Doppler shifted to green. So the judge decides to fine him $1 for every kilometer per second he is going over the speed limit. Assume that the shift between red and green in the spectrum is 500 Angstroms. How much is his fine?

 

  1. About $3,000.
  2. About $30,000.
  3. About $5.000.
  4. About $300,000.
  5. About $186,000.
 


 

28. Suppose the temperature of the surface of a star were to rise. How would this affect the star's color and the wavelength of the lines seen in its spectrum?

 

  1. The color and the lines both shift to shorter wavelength.
  2. The lines shift to longer wavelengths, the color doesn't change.
  3. The lines and color both shift to longer wavelengths.
  4. The lines that are seen would show no systematic change to longer or shorter wavelengths.
  5. The color shifts to a longer wavelength, the lines that are seen would show no systematic change to either longer or shorter wavelengths.
 


 

29. Which of the following has the stellar spectral classes correctly ordered from coolest to hottest?

 

  1. ABCDEFG
  2. ABFGKMO
  3. FGKOBAM
  4. MKGFABO
  5. OBAFGKM
 


 

30. You would expect to find the highest degree of ionization in the atmosphere of

 

  1. the Sun.
  2. an A-type main-sequence star.
  3. an M-type long period variable.
  4. an O-type star.
  5. a planet like Venus.
 


 

31. If a star has weak hydrogen lines but strong lines of molecules in its spectrum, it should be a

 

  1. fairly cool star.
  2. very large star.
  3. very hot star.
  4. very old star.
  5. freak, since no such stars are known to exist.
 


 

32. We can measure the temperatures of stars from a study of their

 

  1. velocities.
  2. brightnesses.
  3. spectra.
  4. colors.
  5. Both D and C
 


 

33. In what kind of star listed below does one see strong absorption lines due to ionized helium?

 

  1. A
  2. O
  3. G
  4. K
  5. M
 


 

34. Why do hotter stars show fewer molecular absorption features than cooler stars?

 

  1. In hot stars, the molecules suffer energetic collisions with atoms in the stellar atmosphere and are torn apart.
  2. In hot stars, the molecules absorb energetic photons and their component atoms fly apart, having too much energy to stay bound.
  3. In hot stars, the molecules are collisionally dissociated.
  4. In hot stars, the molecules are photodissociated.
  5. All of the statements above are correct.
 


 

35. The spectral type of the Sun is

 

  1. K.
  2. G.
  3. F.
  4. A.
  5. B.
 


 

36. If the Balmer (hydrogen) lines are very weak in the spectrum of a star, then we could conclude that (choose the best answer)

 

    1. it is very hot.
    2. it is very cool.
    3. it is either very hot or very cool.
    4. it has lots of hydrogen.
    5. it has little hydrogen
 


 

37. Imagine a star travelling at a speed of 600 km/sec, perpendicular to the line of sight from the Earth to the star. An astronomer on Earth would observe the hydrogen spectral line at 4861 Angstroms at a wavelength of

 

  1. 4855 Angstroms
  2. 4860 Angstroms
  3. 4851 Angstroms
  4. 4861 Angstroms
  5. 4871 Angstroms

 

38. Captain Picard of the USS Enterprise is traveling toward the Earth at one-half the speed of light. He sends a message to Earth, using light with a wavelength of 4000 Angstroms. At what wavelength will the message be observed on Earth

 

    1. 4000 Angstroms
    2. 6000 Angstroms
    3. 2000 Angstroms
    4. 3600 Angstroms
    5. 4400 Angstroms
 


 

39. An object has lines of titanium oxide and ionized helium in its spectrum. What should the observer conclude?

 

  1. There must be an error; such an observation is not possible.
  2. It is a very hot star that also has an unusually high abundance of Ti
  3. The "star" is an actually an unresolved binary system; one star is very hot and one is very cold
  4. It is a hot star and the TiO lines are absorbed by a dark interstellar cloud between earth and the star
  5. It is a cool star with an overabundance of helium in its composition
 


 

40. What quantity has the biggest influence in determining the spectral type of a star?

 

  1. its chemical composition
  2. its pressure
  3. its magnetic field
  4. its surface temperature
  5. its size
 


 

41. A star whose parallax is 1 second of arc is at a distance of

 

  1. 1 parsec
  2. 10 parsecs
  3. 100 parsecs
  4. 0.1parsecs
  5. 1 light year
 


 

42. If a star is observed from Earth to have a parallax of 0.25 seconds of arc, what would the parallax be if the star were observed from telescopes in Saturn's orbit, which is 10 times larger? (Hint: a drawing may be helpful)

 

  1. the same, 0.25 seconds of arc
  2. 10 times larger, 2.5 seconds of arc
  3. 100 (10 squared) times larger, 25 seconds of arc
  4. 10 times smaller, 0.025 seconds of arc
  5. 100 (10 squared) times smaller, 0.0025 seconds of arc
 


 

43. In the H-R diagram, a star less luminous and hotter than the Sun would be found

 

  1. below and to the left of the Sun
  2. above and to the left of the Sun
  3. below and to the right of the Sun
  4. above and to the right of the Sun
  5. at the top end of the main sequence
 


 

44. If two normal stars have the same surface temperature, yet star A has a lower luminosity than star B, then

 

  1. A must be larger than B
  2. A must be smaller than B
  3. A is emitting non-thermal energy
  4. not enough information to say
 


 

45. The constellation Gatorius consists of five stars, all of which appear equally bright to the eye. Star A is an O supergiant, B is an M giant, C is an M main sequence star, D is a G main-sequence star, and E is a B white dwarf. Which star is intrinsically the most luminous?

 

  1. A
  2. B
  3. C
  4. D
  5. E
 


 

46. The constellation Gatorius shown in the above figure consists of five stars, all of which appear equally bright to the eye. Star A is an O supergiant, B is an M giant, C is an M main sequence star, D is a G main-sequence star, and E is a B white dwarf. Which star is the farthest from us?

 

  1. A
  2. B
  3. C
  4. D
  5. E
 


 

47. Into which category do the majority of stars fall?

 

  1. red giants
  2. white dwarfs
  3. main sequence
  4. supergiants
  5. hotter than the Sun
 


 

48. The Hertzsprung-Russell diagram is

 

  1. a graph of stellar luminosity versus stellar mass.
  2. a graph of surface temperature versus stellar mass
  3. a plot of the color of a star versus its surface temperature
  4. a graph of stellar luminosity versus surface temperature
  5. a graph of luminosity versus apparent brightness