Study Questions - Set 2B
Chapter 6

1.	As light passes from air into a dense but transparent material it A. speeds up. B. slows down. C. maintains its speed. D. changes its speed to the speed of sound in glass.

2.

What is the refraction of light? A. the change in direction of a light ray as it reflects from a more dense material than the one in which it is traveling B. the absorption of light as it traverses a dense, transparent material C. the breaking of white light into its composite colors D. the change in direction of a light ray as it crosses from a less dense, transparent material to a more dense one

3.	Which characteristic of a glass lens is the most important in bending light rays to form a focused image? A. curvature and shape of its surfaces B. color of the glass C. diameter or size of the lens D. thickness of the center of the lens

4.	The main optical element in a refracting telescope is a A. lens. B. mirror. C. combination of many small plane mirrors. D. prism of glass.

5.	Who was the first astronomer to build and use a telescope to observe the night sky? A. Copernicus B. Newton C. Tycho Brahe D. Galileo

6.	The major reason astronomers seek funds to build larger telescopes is to A. bring stars closer to Earth. B. measure a wider spectrum of light from stars. C. provide magnified images of stars. D. collect more light from distant objects.

7.

For many years, the Palomar telescope (5 m diameter) in California was the largest fully steerable telescope in the world; now that honor falls to one of the two Keck telescopes (each of diameter 10 m) in Hawaii. How many times larger is the light-gathering power of the Keck telescope than the Palomar telescope? A. 2 times larger B. 4 times larger C. 1.4 times larger D. 8 times larger

8.

In a correctly focused refracting telescope, the objective lens and the eyepiece lens are separated by a distance equal to the (see Fig. 6-5, Freedman and Kaufmann, Universe, 6th ed.) A. focal length of the eyepiece. B. focal length of the objective minus the focal length of the eyepiece. C. sum of the focal lengths of objective and eyepiece. D. focal length of the objective.

9.	Which of the following types of telescope will suffer from chromatic aberration unless very expensive measures are taken to avoid it? A. radio telescope B. cassegrain telescope C. reflecting telescope D. refracting telescope

10.

Chromatic aberration occurs in a refracting telescope when A. some wavelengths are reflected from the front surface of the objective lens of the telescope. B. light from some wavelengths is absorbed by the lenses, thereby creating false colors of objects. C. the lenses bend under their own weight, thereby distorting the final image. D. all colors of light do not come to the same focal point.

11.

If you want to build a telescope having the least possible amount of chromatic aberration, you should use A. mirrors instead of lenses. B. as thin a front lens as possible. C. a front lens that has been coated with a special material to reduce refraction. D. a front lens that is composed of two closely spaced lenses made of different kinds of glass.

12.

When a ray of light strikes a smooth mirror surface at an angle to the perpendicular, the ray is reflected A. at various angles, depending on wavelength. B. back along its original (incoming) path. C. so that it travels along the perpendicular to the surface of the mirror. D. on the "other" side of the perpendicular but at the same angle as the incoming ray.

13.

How is a Newtonian reflecting telescope constructed? A. A series of mirrors channel the light to a remote location. B. It has a concave primary mirror and flat, diagonal secondary mirror. C. A concave primary mirror, with a concave secondary mirror that reflects light back through a hole in the primary mirror. D. A concave primary mirror, with a convex secondary mirror that reflects light back through a hole in the primary mirror.

14.	When light from the concave primary mirror of a telescope is reflected by a small secondary mirror through a hole in the primary, it is called A. prime focus. B. Newtonian focus. C. Cassegrain focus. D. Coude focus.

15.

If part of the primary mirror of a reflecting telescope is blocked off by a small screen, which of the following characteristics of the final image is affected? A. Although the brightness is unaffected, the size of the image will be reduced. B. A part of the image is missing. C. Only the brightness is reduced. D. Depending on which part of the mirror is obscured, the color of the image is affected.

16.	To produce the sharpest images of very distant objects, the best shape for the cross-section of a large astronomical mirror should be A. elliptical. B. spherical. C. perfectly flat and smooth. D. parabolic.

17.

A spherical mirror suffers from spherical aberration because A. the starlight is distorted by turbulence in the Earth's atmosphere. B. the mirror sags under its own weight, distorting the image. C. different parts of the mirror focus the light at different distances from the mirror. D. different colors are focused at different distances from the mirror.

18.

The primary mirror in the 10-m Keck telescope is made from A. one large, thin slab of glass whose surface is continuously adjusted by computer-controlled motors. B. 36 individual mirrors, mounted so that they all bring the light to the same focus. C. six individual mirrors mounted so that they all bring the light to the same focus. D. one large slab of glass made very thick to avoid sagging.

19.

In telescopes, the resolution is worse for A. larger diameter lenses or mirrors and shorter wavelength light (or other electromagnetic radiation). B. smaller diameter lenses or mirrors and longer wavelength light (or other electromagnetic radiation). C. smaller diameter lenses or mirrors and shorter wavelength light (or other electromagnetic radiation). D. larger diameter lenses or mirrors and longer wavelength light (or other electromagnetic radiation).

20.

At the extreme limit of magnification, the major cause of blurred and unsharp images of objects observed through very large telescopes is A. the poor tracking capabilities of modern telescopes. B. air turbulence in the Earth's atmosphere. C. the poor optical polish achievable on large mirrors. D. the clumsiness of the telescope operator.

21.

It is difficult to improve the angular resolution of optical telescopes located on the surface of the Earth beyond a certain limit because A. we would need to build larger telescopes and this is very expensive. B. spherical mirrors suffer from too much aberration. C. air turbulence distorts the star images more than does the telescope optics. D. large telescopes are always reflecting telescopes and these suffer from too much chromatic aberration.

22.

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? 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

23.	The detector that in many instances has replaced the photographic plate for astronomical photography is the A. diffraction grating. B. CCD (charge-coupled device). C. interferometer. D. PMT (photomultiplier tube).

24.

The charged-coupled device (CCD), now used extensively for astronomical imaging, works on what principle? A. Light generates electrical charge on a computer-readable, multi-element array of detectors. B. Light from the image modifies the plastic material on a disk, which can then be read on a standard video compact disk (CD) player. C. Light from the image is detected by new, high-sensitivity, fine-grain, automatically processed film. D. A single optical detector generates an electrical signal as it is scanned quickly across the astronomical image.

25.	A spectrograph is usually used in astronomy to measure the A. variation of the mass of an object as it moves through space. B. distribution of light intensity among the various colors. C. vibration of Earth following an earthquake. D. brightness of light at one specific color.

26.

How does angular resolution for a given diameter of telescope depend on wavelength? A. Angular resolution worsens as wavelength increases. B. Angular resolution improves as wavelength increases. C. Angular resolution may improve or worsen as wavelength increases, depending on other factors such as intensity and spectral range (e.g., optical, infrared, radio). D. Angular resolution depends only on the diameter of the telescope and is independent of wavelength.

27.

The angular resolution attainable with a radio telescope, compared to that attainable with an optical telescope of the same diameter, is significantly inferior because A. the wavelength of radio waves is larger than that of visible light. B. it is difficult to make a reflector for radio waves since these waves penetrate most materials. C. the Earth's atmosphere disturbs radio waves from space much more than it does visible light. D. radio wavelengths are smaller than visible wavelengths, making it difficult to produce a reflector sufficiently smooth to produce images.

28.

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

29.	The two ranges of electromagnetic radiation for which Earth's atmosphere is reasonably transparent are A. UV and radio waves. B. visible and far infrared radiation. C. X rays and visible radiation. D. visible and radio radiation.

30.

Astronomy from space vehicles is particularly useful because the telescope A. is in a clean, dust-free environment and scattered light is much reduced. B. is above Earth's absorbing and distorting atmosphere and can measure radiation over a very wide wavelength range. C. is in a gravity-free state, its mirror is not distorted by gravitational stress, and it can produce sharper images. D. moves smoothly in a constant orbit and can produce sharp photographs.

31.	For which of the following spectral ranges is it essential that astronomical observations be made from space? A. visible B. far UV C. radio D. near infrared

32.	After the Hubble Space Telescope was launched, it was found to suffer seriously from A. chromatic aberration. B. spherical aberration. C. too much angular resolution. D. jittery images caused by strong stratospheric winds.

33.	The first nonvisible radiation detected from outer space was A. X rays. B. radio waves. C. gamma rays. D. ultraviolet (UV) light.

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