Question 1

Telescopes are placed in space to view distant galaxies primarily to:

Accepted Answer

A) get closer to the observed objects. 
B) avoid having to steer the telescope against Earth's motion. 
C) avoid the absorption of the light or other radiations in the atmosphere of Earth. 
D) avoid the light pollution from Earth's populated areas. 
A) get closer to the observed objects. 
B) avoid having to steer the telescope against Earth's motion. 
C) avoid the absorption of the light or other radiations in the atmosphere of Earth. 
D) avoid the light pollution from Earth's populated areas.

Question 2

How many times more light can the 10-m diameter Keck telescope on Mauna Kea in Hawaii collect than an average unaided human eye, which has a typical aperture diameter of 5 mm?

Accepted Answer

A) 2 × 104 
B) 2000 
C) 4 × 106 
D) 4 
A) 2 × 104 
B) 2000 
C) 4 × 106 
D) 4

Question 3

Approximately what percentage of the light falling on a typical photographic plate from a telescope is actually used to record an image on this plate?

Accepted Answer

A) 25% 
B) 50% 
C) 98% 
D) 2% 
A) 25% 
B) 50% 
C) 98% 
D) 2%

Question 4

During the past few decades a number of techniques have been developed to enhance the performance of optical and radio telescopes. These include all of the following except one. Which one is the exception?

Accepted Answer

A) placing optical telescopes in orbit above the atmosphere 
B) building lens telescopes comparable in size to the largest mirror telescopes (approximately 10 m) 
C) computer connections allowing radio telescopes thousands of miles apart to be used in unison 
D) adaptive optics, allowing the shape of a telescope mirror to be changed rapidly to compensate for atmospheric turbulence 
A) placing optical telescopes in orbit above the atmosphere 
B) building lens telescopes comparable in size to the largest mirror telescopes (approximately 10 m) 
C) computer connections allowing radio telescopes thousands of miles apart to be used in unison 
D) adaptive optics, allowing the shape of a telescope mirror to be changed rapidly to compensate for atmospheric turbulence

Question 5

A thick lens is able to bend light more than a thin lens. What, if anything, can you say about the focal lengths?

Accepted Answer

A) The thick lens has the longer focal length. 
B) The thin lens has the longer focal length. 
C) Focal length is determined by the focal point for parallel light and has nothing to do with lens thickness. 
D) To determine relative focal length, you would have to know both the lens thickness and the light wavelength. 
A) The thick lens has the longer focal length. 
B) The thin lens has the longer focal length. 
C) Focal length is determined by the focal point for parallel light and has nothing to do with lens thickness. 
D) To determine relative focal length, you would have to know both the lens thickness and the light wavelength.

Question 6

To compensate for atmospheric distortion using adaptive optics, a bright object must serve as a target. How is this accomplished?

Accepted Answer

A) Adaptive optics can only be used when a bright star is in the field of view. 
B) Sunlight reflecting from artificial satellites serves as the target. 
C) Adaptive optics can only be used on very powerful telescopes for which even faint stars can be used as targets. 
D) Lasers are used to excite sodium atoms in the upper atmosphere to glow and serve as a target. 
A) Adaptive optics can only be used when a bright star is in the field of view. 
B) Sunlight reflecting from artificial satellites serves as the target. 
C) Adaptive optics can only be used on very powerful telescopes for which even faint stars can be used as targets. 
D) Lasers are used to excite sodium atoms in the upper atmosphere to glow and serve as a target.

Question 7

When white light passes through a prism or a lens, which wavelengths of light are deflected most by the glass?

Accepted Answer

A) The directions of all wavelengths are changed by the same amount. 
B) The intermediate wavelengths. 
C) The longer wavelengths. 
D) The shorter wavelengths. 
A) The directions of all wavelengths are changed by the same amount. 
B) The intermediate wavelengths. 
C) The longer wavelengths. 
D) The shorter wavelengths.

Question 8

For optical telescopes, we want light to reflect from the mirror more or less back along the direction of incidence. If we are detecting radiation that strikes the mirror at a grazing angle, then we are observing:

Accepted Answer

A) radio waves. 
B) ultraviolet waves. 
C) x rays. 
D) gamma rays. 
A) radio waves. 
B) ultraviolet waves. 
C) x rays. 
D) gamma rays.

Question 9

The Very Large Array (VLA) built in New Mexico provides very sharp radio images of astronomical sources by combining the signals from many individual telescopes. It consists of:

Accepted Answer

A) 85 units. 
B) 2 units. 
C) 3 units. 
D) 27 units. 
A) 85 units. 
B) 2 units. 
C) 3 units. 
D) 27 units.

Question 10

What is a charge-coupled device (CCD)?

Accepted Answer

A) a very fine grained photographic film that can be "read" electronically 
B) an extremely sensitive thermocouple that records the temperature increase every time a photon hits it 
C) a spectrometer that has been made especially sensitive by using a grating with over one million lines per centimeter 
D) an array of electronic sensors that record the charge buildup due to photon absorption 
A) a very fine grained photographic film that can be "read" electronically 
B) an extremely sensitive thermocouple that records the temperature increase every time a photon hits it 
C) a spectrometer that has been made especially sensitive by using a grating with over one million lines per centimeter 
D) an array of electronic sensors that record the charge buildup due to photon absorption

Question 11

In spectroscopy, a diffraction grating is a:

Accepted Answer

A) screen placed at the focus of a telescope to provide a calibrated grid on photographs. 
B) source of light that provides calibration lines alongside the measured spectrum. 
C) piece of glass or metal on which many closely spaced grooves have been cut. 
D) prism of very pure glass through which light can pass. 
A) screen placed at the focus of a telescope to provide a calibrated grid on photographs. 
B) source of light that provides calibration lines alongside the measured spectrum. 
C) piece of glass or metal on which many closely spaced grooves have been cut. 
D) prism of very pure glass through which light can pass.

Question 12

Each of the following is a technique used by astronomers to increase the amount of detail that can be seen or photographed through telescopes except one. Which is the exception?

Accepted Answer

A) antireflective coatings, where the mirror is coated with a substance, such as fluorite, to reduce the amount of reflected light 
B) increased size, where mirrors are made far larger than was possible before, e. g., 8 to 10 m in diameter and larger 
C) adaptive optics, where the tilt and shape of mirrors in the telescope are changed many times per second to compensate for atmospheric turbulence 
D) multiple-mirror telescopes, where several mirrors are mounted together in a single telescope to simulate the performance of a single, very large mirror 
A) antireflective coatings, where the mirror is coated with a substance, such as fluorite, to reduce the amount of reflected light 
B) increased size, where mirrors are made far larger than was possible before, e. g., 8 to 10 m in diameter and larger 
C) adaptive optics, where the tilt and shape of mirrors in the telescope are changed many times per second to compensate for atmospheric turbulence 
D) multiple-mirror telescopes, where several mirrors are mounted together in a single telescope to simulate the performance of a single, very large mirror

Question 13

Compared to the speed of visible light in a vacuum (or in space), its speed in glass is:

Accepted Answer

A) greater. 
B) less. 
C) exactly the same. 
D) much greater. 
A) greater. 
B) less. 
C) exactly the same. 
D) much greater.

Question 14

An optical telescope using 650-nm light has a diameter of 1 m. A radio telescope using radio waves of wavelength 6.5 cm has a diameter of 100 m. The resolution of the optical telescope is:

Accepted Answer

A) better than that of the radio telescope by a factor of 1000. 
B) worse than that of the radio telescope by a factor of 1000. 
C) better than that of the radio telescope by a factor of 100,000. 
D) worse than that of the radio telescope by a factor of 100,000. 
A) better than that of the radio telescope by a factor of 1000. 
B) worse than that of the radio telescope by a factor of 1000. 
C) better than that of the radio telescope by a factor of 100,000. 
D) worse than that of the radio telescope by a factor of 100,000.

Question 15

What is the main reason for combining many radio telescopes together into an interferometer with large distances between telescopes?

Accepted Answer

A) to obtain much sharper images of sources 
B) to ensure that at least one of the telescopes is in a radio interference-free zone 
C) to ensure that observations are uninterrupted by the failure of one or two telescopes 
D) to collect more radiation from very faint sources 
A) to obtain much sharper images of sources 
B) to ensure that at least one of the telescopes is in a radio interference-free zone 
C) to ensure that observations are uninterrupted by the failure of one or two telescopes 
D) to collect more radiation from very faint sources

Question 16

At the mirror of a reflecting telescope, the light reflects from a coated surface rather than refracting through a lens. This eliminates:

Accepted Answer

A) spherical aberration. 
B) chromatic aberration. 
C) coma. 
D) astigmatism. 
A) spherical aberration. 
B) chromatic aberration. 
C) coma. 
D) astigmatism.

Question 17

A refracting telescope has an objective lens of focal length 80 cm, a diameter of 10 cm, and an eyepiece of focal length 5 cm and diameter 1 cm. How much more light will this telescope collect than the average unaided eye, whose focal length is 2 cm and diameter is 0.5 cm?

Accepted Answer

A) 4 
B) 1600 
C) 20 
D) 400 
A) 4 
B) 1600 
C) 20 
D) 400

Question 18

In the reflection of a light beam from a flat mirror, the angle between the incident and reflected beams relative to the perpendicular to the surface of the mirror is:

Accepted Answer

A) equal to the angle between the incident beam and the perpendicular. 
B) equal to 1/2 the angle between the incident beam and the perpendicular. 
C) always a right angle, or 90°. 
D) twice the angle between incident beam and the perpendicular. 
A) equal to the angle between the incident beam and the perpendicular. 
B) equal to 1/2 the angle between the incident beam and the perpendicular. 
C) always a right angle, or 90°. 
D) twice the angle between incident beam and the perpendicular.

Question 19

A Newtonian telescope uses:

Accepted Answer

A) two curved mirrors. 
B) several mirrors, some curved, some flat, to guide light to a fixed focus with respect to Earth. 
C) one curved mirror and one flat mirror at a 45° angle to the curved mirror. 
D) only one mirror. 
A) two curved mirrors. 
B) several mirrors, some curved, some flat, to guide light to a fixed focus with respect to Earth. 
C) one curved mirror and one flat mirror at a 45° angle to the curved mirror. 
D) only one mirror.

Question 20

What factor has seriously reduced the effectiveness of the telescopes around the world, such as those at Mt. Palomar in California and at Kitt Peak, near Tucson, Arizona, over the last few years?

Accepted Answer

A) tarnishing of the mirror surface by air pollution 
B) cracking of the mirror by earthquakes 
C) bending of the mirror surface from repeated exposure to the cold night air 
D) light scattering in the atmosphere from nearby cities 
A) tarnishing of the mirror surface by air pollution 
B) cracking of the mirror by earthquakes 
C) bending of the mirror surface from repeated exposure to the cold night air 
D) light scattering in the atmosphere from nearby cities

Exam 6: Optics and Telescopes

Telescopes are placed in space to view distant galaxies primarily to:

How many times more light can the 10-m diameter Keck telescope on Mauna Kea in Hawaii collect than an average unaided human eye, which has a typical aperture diameter of 5 mm?

Approximately what percentage of the light falling on a typical photographic plate from a telescope is actually used to record an image on this plate?

During the past few decades a number of techniques have been developed to enhance the performance of optical and radio telescopes. These include all of the following except one. Which one is the exception?

A thick lens is able to bend light more than a thin lens. What, if anything, can you say about the focal lengths?

To compensate for atmospheric distortion using adaptive optics, a bright object must serve as a target. How is this accomplished?

When white light passes through a prism or a lens, which wavelengths of light are deflected most by the glass?

For optical telescopes, we want light to reflect from the mirror more or less back along the direction of incidence. If we are detecting radiation that strikes the mirror at a grazing angle, then we are observing:

The Very Large Array (VLA) built in New Mexico provides very sharp radio images of astronomical sources by combining the signals from many individual telescopes. It consists of:

What is a charge-coupled device (CCD)?

In spectroscopy, a diffraction grating is a:

Each of the following is a technique used by astronomers to increase the amount of detail that can be seen or photographed through telescopes except one. Which is the exception?

Compared to the speed of visible light in a vacuum (or in space), its speed in glass is:

An optical telescope using 650-nm light has a diameter of 1 m. A radio telescope using radio waves of wavelength 6.5 cm has a diameter of 100 m. The resolution of the optical telescope is:

What is the main reason for combining many radio telescopes together into an interferometer with large distances between telescopes?

At the mirror of a reflecting telescope, the light reflects from a coated surface rather than refracting through a lens. This eliminates:

A refracting telescope has an objective lens of focal length 80 cm, a diameter of 10 cm, and an eyepiece of focal length 5 cm and diameter 1 cm. How much more light will this telescope collect than the average unaided eye, whose focal length is 2 cm and diameter is 0.5 cm?

In the reflection of a light beam from a flat mirror, the angle between the incident and reflected beams relative to the perpendicular to the surface of the mirror is:

A Newtonian telescope uses:

What factor has seriously reduced the effectiveness of the telescopes around the world, such as those at Mt. Palomar in California and at Kitt Peak, near Tucson, Arizona, over the last few years?

Astronomy and the Universe

Knowing the Heavens

Eclipses and the Motion of the Moon

Gravitation and the Waltz of the Planets

The Nature of Light

Comparative Planetology I: Our Solar System

Comparative Planetology II: the Origin of Our Solar System

The Living Earth

Our Barren Moon

Mercury, Venus, and Mars: Terrestrial, yet Unique

Jupiter and Saturn: Lords of the Planets

Jupiter and Saturns Satellites of Fire and Ice

Uranus, Neptune, Pluto, and the Kuiper Belt: Remote Worlds

Asteroids, Comets, and Impacts

Our Star, the Sun

The Nature of the Stars

The Birth of Stars

Stellar Evolution: on and After the Main Sequence

Stellar Evolution: The Death of Stars

Stellar Remnants: Neutron Stars and Black Holes

Our Galaxy

Galaxies

Quasars and Active Galaxies

Cosmology: The Origin and Evolution of the Universe

Exploring the Early Universe

The Search for Extraterrestrial Life

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