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How many photons are emitted per second by a 100 W light bulb, assuming they all come out at 600 nm (which corresponds to a frequency of 5 x 10^14 Hz)?
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3 x 10^21 photons per second
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What produces the energy emitted by the Sun?
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Protons fusing into Helium nuclei.
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Based on their respective collecting areas, how much more sensitive would you expect the 300m Arecibo telescope to be relative to the 100m Green Bank Telescope?
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9 times as sensitive
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If a laser emitting at 600 nm is observed to be emitting at 606 nm, how fast is it moving with respect to the observer?
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0.01 times the speed of light, away from the observer.
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Two stars orbiting each other are separated by 2 AU, at a distance of 80 pc away from us. How large a space telescope would we need to resolve the two stars, assuming diffraction limited optics at 2 microns? Hint: a pc is about 200,000 AU.
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12 meters
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When does a hydrogen atom emit a Balmer-alpha photon (a 656 nm photon)?
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When its electron descends in energy from an n=3 state to an n=2 state.
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Does 900 nm wavelength light have a higher frequency or lower frequency than 450 nm wavelength light, and by how much?
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The 900 nm wavelength light has lower frequency, by a factor of two.
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If the Earth were twice as massive as it is, but at the same radius around the Sun, how would the length of the year change?
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It would not change.
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The tendency of a wave to bend as it passes from one transparent medium to another (like from air to glass) is called...
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...refraction.
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Which of the following is constant for all types of light waves traveling in a vacuum?
Frequency, Wavelength, Energy, Speed.
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Speed
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What information is necessary to infer the radius of a star?
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Color, flux, and distance.
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What is the mathematical relationship between flux f, luminosity L, and distance D? Hint: luminosity is in units Joules/second, flux is in units Joules/second/meter^2, and distance is in units of meters.
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f = L/[4(pi)D^2]
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What is the diffraction limit of a 2.5m telescope in space at 400 nm?
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0.025 arcsec
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The surface of the Sun is closest to what temperature?
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6000 K
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Is the peak wavelength of emission of a star with a surface temperature of 5000K longer or shorter than that of a star at 10,000K, and by how much?
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Longer, by a factor of two.
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How does the lifetime of stars depend on their mass?
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Less massive stars live longer.
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The Moon's mass is 7.4 x 10^22 kg and its radius is 1,700 km. What is the speed of a spacecraft moving in a circular orbit 300 km above the surface of the moon?
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1500 m/s
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How are the color (and thus temperature T) and luminosities of Main Sequence stars related?
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Bluer stars are much more luminous (L is directly proportional to T^4)
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What is the mean density of the Sun compared to that of water?
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Equally dense.
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A person is standing 100 meters away from you. How large an angular size do they appear to have?
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About 1 degree.
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How short a wavelength does a photon have to have to ionize a hydrogen (eject its electron)?
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Less than 91.2 nm
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What is the maximum angular resolution possible from a ground based optical telescope that isn't using adaptive optics?
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Around 1 arcsec.
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How far away is the star Spica, whose parallax is 0.01 arcsec?
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100 pc
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Vega is about 100 time brighter than the faintest stars your eye can detect, and is about 8 pc away. How far away would it have to be to be undetectable by your eye?
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About 80 pc
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What is the wavelength corresponding to the peak of the blackbody curve for dust that is 10 K in temperature?
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0.3 mm
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How does the radius of red giant stars compare to the radius of dwarf stars of the same color?
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Red giants are much larger in radius than dwarfs of the same color.
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In Bohr's model of the atom, electrons:
A. only make transitions between orbitals of specific energies.
B. are not confined to specific orbits.
C. move from orbit to orbit in many small steps.
D. can be halfway between orbits.
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A. Only make transitions between orbitals of specific energies
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Why are most large telescopes reflectors, not refractors?
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Large lenses deform under their own weight, but mirrors can be suspended.
Reflectors do not suffer from chromatic aberration as refractors do.
Large, very clear lenses are harder to produce than mirrors.
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Which of the following is ordered from lowest to highest frequency of light?
A. Ultraviolet, X-ray, infrared, radio, optical.
B. Optical, infrared, radio, X-ray, ultraviolet
C. X-ray, ultraviolet, optical, infrared, radio.
D. Radio, infrared, optical, ul
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D. Radio, infrared, optical, ultraviolet, X-ray.
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What is the lifetime of stars like the Sun?
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10 billion years
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What is the most common element in the universe?
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Hydgrogen (H)
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What is the speed of light?
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300,000 km/s
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What is the range of wavelengths of light that your eye can detect?
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400 to 900 nm
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If the angular resolution of a 1 meter telescope in space is 0.25 arcsec (for 1 micron wavelength light), what would the angular resolution of a 2.5 meter telescope in space (like the Hubble Space Telescope) be?
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0.10 arcsec
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At a temperature of 5800 K, hydrogen atoms in the solar atmosphere have typical random speeds of about 12 km/s. Assuming that spectral line broadening is just the result of the Doppler broadening due to these random motions, what is the thermal width of t
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About 0.05 nm
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