Download Quiz # 3

Introduction to Descriptive Astronomy
Summer 2012
Quiz # 3
Name: __________________________
1. The major reason astronomers seek funds to build larger telescopes is to
A) measure a wider spectrum of light from stars.
B) collect more light from distant objects.
C) provide magnified images of stars.
D) bring stars closer to the Earth.
2. The light-gathering power of a telescope depends directly on the
A) area of the final aperture of its eyepiece.
B) focal length of its primary mirror or lens.
C) ratio of the focal lengths of its primary element (mirror or lens) and its eyepiece.
D) area of its primary mirror or lens.
3. Which of the following characteristics of an astronomical telescope is the most important for determining
the angular resolution?
A) magnifying power of the telescope
B) focal length of the objective lens or mirror
C) focal length of the eyepiece
D) diameter of the objective lens or mirror
4. What percentage of the light falling on the best CCDs is typically wasted (does not contribute to the
formation of the image)?
A) 1%
B) 10%
C) 90%
D) 98%
5. Spherical aberration can be corrected or avoided in a reflecting telescope by
A) grinding the mirror to a more accurate spherical curve.
B) grinding the mirror to a parabolic shape.
C) using light of only one color.
D) grinding the mirror to an elliptical shape.
6. When a light ray in air or a vacuum hits the surface of a piece of perfectly smooth, flat glass at an angle
and enters the glass, it will
A) reverse its direction and return along its original path.
B) bend toward the perpendicular to the surface.
C) bend away from the perpendicular to the surface.
D) not change its direction at all.
7. What is chromatic aberration in a telescope?
A) Light of different colors reflecting from the objective mirror of the telescope comes to a focus at
different points in front of the mirror.
B) Light of different colors comes to a focus at different points behind the objective lens inside the
telescope.
C) Light striking the lens at different distances from the center of the lens comes to a focus at different
points inside the telescope.
D) The objective lens varies in thickness from center to edge, and light passing through the different
thicknesses suffers different amounts of absorption, thereby coloring the image.
8. If one observatory site is described as having better “seeing” than another observatory site, what is it that
is better at the first site?
A) The sky is more transparent and there is less haze in the atmosphere at that site, providing brighter
and sharper images.
B) The winds are lighter at the better site, thereby producing less telescope vibration.
C) There is less air turbulence at that site, causing less twinkling and blurring of the images.
D) There are more clear nights at that site.
9. One technique that astronomers are now using to increase the amount of detail that can be recorded with
telescopes is
A) spinning huge tubs of mercury, thus producing very large parabolic surfaces at relatively low cost.
B) antireflective coatings, where the mirror is coated with a substance such as calcium fluorite to
reduce the amount of reflected light.
C) increased size, with mirrors up to 10 m in diameter (far larger than at earlier times), thereby
producing greater intrinsic angular resolution.
D) adaptive optics, where the tilt and shape of mirrors in the telescope are changed many times per
second to compensate for atmospheric turbulence.
10. One major difference between radio waves and light is that
A) light waves are electromagnetic, whereas radio waves are not.
B) radio waves are electromagnetic, whereas light waves are not.
C) radio waves have shorter wavelength than light waves.
D) radio waves have longer wavelength than light waves.
11. In telescopes designed for any wavelength of electromagnetic radiation, the angular resolution is worse
for
A) larger diameter lenses or mirrors or radio dishes and longer wavelength radiation.
B) larger diameter lenses or mirrors or radio dishes and shorter wavelength radiation.
C) smaller diameter lenses or mirrors or radio dishes and shorter wavelength radiation.
D) smaller diameter lenses or mirrors or radio dishes and longer wavelength radiation.
12. Astronomy from space vehicles is particularly useful because the telescope
A) is in a gravity-free state; the mirror is not distorted by gravitational stress and can therefore produce
sharper images.
B) moves smoothly and without vibration in a constant orbit and can therefore produce sharp
photographs.
C) is above the Earth's absorbing and distorting atmosphere and can measure radiation over a very
wide wavelength range.
D) is in a clean, dust-free environment and scattered light is much reduced.
13. The New Zealand physicist Lord Rutherford and his colleagues in England demonstrated the existence of
the very small but massive nucleus inside every atom in which crucial experiment?
A) deflection and occasional reflection backward of energetic nuclear particles from a beam aimed at a
thin metal sheet
B) measurement of the spectrum of light emitted from a thin, heated metal sheet
C) detection of the motion of electrons around the nucleus by the use of a very powerful microscope
D) emission of electrons from a metal surface illuminated with UV light
14. An atom consists of
A) negatively charged electrons moving around a very small but massive, positively charged nucleus.
B) neutrons orbiting an electrically neutral nucleus composed of protons and electrons.
C) positive protons, neutral neutrons, and negative electrons orbiting a small but massive black hole.
D) negatively charged electrons and positively charged protons mixed uniformly throughout the
volume of the atom.
15. In Bohr's model of the hydrogen atom, light is emitted whenever an electron
A) jumps from a lower to an upper energy level or orbit.
B) reverses its direction of motion in its orbit.
C) jumps from an upper to a lower energy level or orbit.
D) spirals into the nucleus.
I pledge that I have acted honorably.
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Answer Key
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
B
D
D
B
B
B
B
C
D
D
D
C
A
A
C