Exam 2 ASTRO
88- The temperature at the top of the clouds on Jupiter is about 165 K. In degrees Celsius, this temperature is
-108°C.
86- The range of temperatures in the Kelvin (absolute) scale between the freezing point and boiling point of water is
100
87- A scientist measures the temperature change between freezing water and boiling water with a thermometer calibrated in the Kelvin or absolute scale. How many degrees Kelvin (K) will he measure?
100
90- Which one of these temperatures is hottest?
100C
40- How much more light can the 5-m telescope at Mount Palomar collect from an astronomical source than can the unaided human eye (with a diameter of 5 mm)?
106 or 1,000,000 times
89- The minimum temperature reached on the surface of Mars, -140°C, is represented on the absolute (Kelvin) temperature scale as
133 K.
38- Many amateur astronomers have telescopes with mirrors 20 cm (1/5 m) in diameter. In comparison, one of the largest astronomical telescopes in the world is the Keck telescope, with a diameter of 10 m. How much greater is the light-gathering power of the Keck telescope than the power of a 20-cm telescope?
2500 times greater
83- The normal temperature of the melting point of water ice is
273 K.
84- On the absolute Kelvin temperature scale, the temperature of freezing water is about
273 K.
17- The speed of light in space is
3 × 10^8 meters per second, independent of the speed of the source.
81- A typical but very cool star might have a temperature of 3100° Celsius. On the Kelvin scale, this is about
3373 K.
85- The temperature of boiling water at ordinary air pressure on the absolute scale—Kelvin—is
373 K.
39- For many years, the Palomar telescope (5-m diameter) in California was the largest telescope in the world; it has now been surpassed by both Keck telescopes (each of diameter 10 m) in Hawaii. How much greater is the light-gathering power of a Keck telescope than that of the Palomar telescope?
4 times greater
41- By what factor is the light-gathering power of the 10-m diameter Keck telescope on Mauna Kea in Hawaii greater than an average unaided human eye, with a typical aperture diameter of 5 mm?
4 × 106 times
Visible wavelengths of electromagnetic radiation have a range of wavelengths of
400 nm to 700 nm.
14- The wavelength of green light is about 500 nanometers. What is this length in meters?
500 billionths of a meter (1 billion = 1000 million)
37- What is the magnification of a Newtonian telescope that has a primary mirror of diameter 0.25 m and focal length of 2 m when used with an eyepiece of focal length 25 mm and an optical diameter of 5 mm?
80 times
11- In terms of wavelengths, gamma rays
have the shortest wavelengths of the named electromagnetic waves.
21- In terms of wavelengths, gamma rays
have the shortest wavelengths of the named electromagnetic waves.
125- The Doppler effect is the
increase in the observed wavelength of light if the source of light is moving away from you.
22- Electromagnetic radiation emitted by a planet has a wavelength of 10 micrometers (1 m = 10-6 m). What name is given to this type of electromagnetic radiation?
infrared radiation
128- When an object is moving away from you, the visible light it emits is Doppler-shifted toward the
infrared.
19- In the photoelectric effect, a beam of light impinges on a metal, and it is observed that electrons are ejected from the metal in greater numbers as the
intensity of the light is increased.
16- All forms of light have what property in common?
All forms of light are electromagnetic radiation.
8- All forms of light have what property in common?
All forms of light are electromagnetic radiation.
42- How can you increase the magnification of a refracting telescope without decreasing the light-gathering power?
Increase the focal length of the eyepiece.
92- If you want to design a device that will detect animals at night by the radiation they give off, even if the night is totally dark, to what wavelength range should you make the device sensitive?
Infrared
93- The hot, dense gas existing on the Sun emits energy
at all wavelengths, with a peak at one particular wavelength (color).
31- Compared to the direction of the incoming light, in which way does the light leave the eyepiece of a Newtonian telescope?
at right angles
23- Radio waves travel through space at what speed?
at the speed of light, 3 × 108 m/s
73- Telescopes are placed in space to view distant galaxies primarily to
avoid the absorption and distortion of the light or other radiations within the atmosphere of the Earth.
72- The main reason for placing a telescope and scientific equipment into an aircraft to carry out infrared astronomy is to
avoid the absorption of the IR radiation by water vapor.
44- As a light ray leaves a glass surface, traveling from the glass back into air at an angle to the surface, the light ray
bends away from the perpendicular to the surface.
10- Visible light occupies what position in the electromagnetic spectrum?
between infrared and ultraviolet
13- The speed of light always has the same value in a vacuum
but is slower in transparent materials such as water and glass.
52- How is spherical aberration usually overcome in the objective lens of a refracting astronomical telescope?
by making the lens very thin, with a long focal length
57- How is chromatic aberration most often corrected in a modern refracting telescope?
by using a combination of two lenses made from different types of glass
68- The first radio energy to be detected from outer space came from the
center of the Milky Way Galaxy, in the direction of Sagittarius
77- When a rod of metal is heated intensely, its predominant color will
change from red through orange to white and then to blue.
96- As a new star evolves from cool dust and gas to a hot star, the peak wavelength of its spectrum of emitted electromagnetic radiation will
change from the infrared to the visible wavelengths.
12- What is refraction of light?
change in direction of a light ray as it passes at an angle from one transparent material to another that has a different optical density
28- What is refraction of light?
change in direction of a light ray as it passes at an angle from one transparent material to another that has a different optical density
122- Because of the Doppler effect, the sound of the engines of an aircraft that flies over us
changes from a high pitch or frequency to a lower pitch.
26- The major reason astronomers seek funds to build larger telescopes is to
collect more light from distant objects.
27- The main reason for building large optical telescopes on the Earth's surface is to
collect more light from faint objects.
32- A Newtonian reflecting telescope is constructed using a
concave primary mirror and a flat, diagonal secondary mirror.
35- A Cassegrain reflecting telescope is constructed using a
concave primary mirror followed by a smaller convex secondary mirror that reflects light back through a hole in the primary mirror.
102- The spectrum of sunlight, when spread out by a spectrograph, has which characteristic appearance?
continuous band of color, crossed by innumerable dark absorption lines
47- Which characteristic property of a glass lens is the most important in bending light rays to form a focused image?
curvature and shape of its surfaces
50- In a telescope, to what does the term aberration refer?
defect in design that blurs or distorts the image
In 1801, Thomas Young performed a crucial experiment on the nature of light when he
demonstrated the wave nature of light by passing light through two slits and obtaining a pattern of bright and dark bands on a screen that he correctly interpreted as interference between the two light beams.
112- The age of the solar system has been dated rather precisely to 4.56 billion years. What method was used to determine this number?
determining the age of meteorites by radioactive dating
101- When light passes through a prism of glass, the
different colors or wavelengths of light are separated in angle by the prism.
51- A lens with spherical surfaces suffers from spherical aberration because
different parts of the lens focus the light at different distances from the lens.
20- Our present understanding of the nature of light is that it
displays behavior of both waves and particles.
104- Spectral lines are of particular importance in astronomy because
each different element has a characteristic line spectrum.
Electromagnetic radiation moving through space with the speed of light consists of oscillating
electric and magnetic fields, always inseparable, always having the same frequency and wavelength and traveling in the same direction.
107- The physical force that holds the components of an atom together is the
electromagnetic attraction between the positive nucleus and the negative electrons.
6- Violet light differs from red light in that it
has a shorter wavelength than red light.
74- Astronomy from space vehicles is particularly useful because the telescope
is above the Earth's absorbing and distorting atmosphere and can measure radiation over a very wide wavelength range.
49- At what distance from the objective lens in a refracting telescope is the primary image formed—that is, at what distance would you place photographic film if you wanted to take a photograph?
its focal length
117- In Bohr's model of the hydrogen atom, light is emitted whenever an electron
jumps from an upper to a lower energy level or orbit.
65- What factor has seriously reduced the effectiveness over the last few years of the 5-m Hale telescope on Mt. Palomar, California, formerly the largest telescope in the world?
light pollution from nearby cities
58- If you want to build a telescope having the least possible amount of chromatic aberration, you should use
mirrors instead of lenses.
94- The star Vega has a higher surface temperature than the Sun. Then with IR indicating infrared and UV indicating ultraviolet, Vega emits _____ IR and _____UV flux than the
more; more;.
123- The Doppler effect is the change in the wavelength of light caused by the source
moving with respect to the observer.
106- An atom consists of
negatively charged electrons moving around a very small but massive, positively charged nucleus.
115- The majority of the mass of ordinary matter resides in the
nuclei of atoms.
108- The position of an element in the periodic table is directly related to the
number of protons in the atomic nucleus and hence to its positive charge.
1- The position of an element in the periodic table, its atomic number, is equal to the
number of protons in the nucleus of the atom.
110- The property of a neutral atom that defines its chemical behavior and fixes its position in the periodic table is
number of protons in the nucleus.
95- An example of an object that emits no radiation at all is any
object at a temperature of 0 K.
118- Electrons in atoms
occupy levels whose energies are fixed.
29- When a ray of light strikes a smooth mirror surface at an angle to the perpendicular, the ray is reflected
on the "other"side of the perpendicular but at the same angle as the incoming ray.
64- The best Earth-based sites for modern large astronomical telescopes, which provide the least seeing effects on astronomical images, are
on the tops of high mountains, above a large fraction of the disturbing atmosphere.
30- A Newtonian telescope uses
one curved mirror and one flat mirror at a 45° angle to the first mirror axis.
34- The prime focus of a reflecting telescope is reached by light after
one reflection.
53- Chromatic aberration is the failure of a telescope objective to bring all colors of light to the same focus and appears in
only a refracting telescope.
124- The observed change in wavelength of light due to the Doppler effect occurs
only when the light source has a radial velocity (i.e., motion toward or away from the observer).
33- The best shape for the cross-section of a simple astronomical mirror in order to produce the sharpest images of very distant objects at its prime focus is a(n)
parabolic shape
99- The light from a small amount of a particular chemical element, when heated in a flame, is found to consist of a
pattern of narrow, bright emissions at wavelengths that are specific to the element and different for each element.
61- Schmidt telescopes are used mostly for
photographing wide areas of the night sky.
69- The primary reason for spreading many radio telescopes across a large area and combining the signals at a central station is to
produce much sharper images of radio sources.
113- Two different isotopes of the element selenium will have the same number of
protons but a different number of neutrons.
111- Isotopes of a particular element in the periodic table have the same number of _____ in the nucleus.¬
protons but different numbers of neutrons
In the 1860s, James Clerk Maxwell carried out important investigations on the nature of light when he
proved mathematically that light could be described by oscillating electric and magnetic fields
91- A blackbody is an idealized object in physics and astronomy that
reflects no light and emits light in a manner determined by its temperature.
48- Which type of telescope uses a lens as the main optical element?
refracting telescope
When light passes through a prism of glass,
refraction changes the directions of different colors or wavelengths of light.
119- What type of spectrum is given off by low-density, high-temperature hydrogen gas?
series of emission lines, spaced in a mathematical sequence
120- When electrons jump from higher levels in hydrogen atoms to the level n = 2, the resulting spectrum will consist of a
series of spectral lines, some of which are in the visible range, the Balmer series.
46- When light passes from air into a dense but transparent material such as glass, it
slows down.
105- Atoms in a thin, hot gas (such as a neon advertising sign), according to Kirchhoff's laws, emit light at
specific wavelengths or colors in a pattern that depends on the element.
100- A spectrograph is a scientific instrument that
spreads out light from a source into its component colors, or spectrum.
80- The Kelvin scale measures
temperature in Celsius-sized degrees above absolute zero.
56- Chromatic aberration occurs in a refracting telescope when
the different colors of light do not focus at the same point.
59- The reason that the primary mirror of an astronomical telescope is often shaped and polished to a parabolic shape is
to avoid spherical aberration by bringing parallel rays to a single focus.
66- Why was adaptive optics developed?
to compensate for image distortion caused by the Earth's atmosphere
70- What is the main reason for using several radio telescopes together as an interferometer?
to obtain much better angular resolution or sharpness in the images
121- According to modern atomic theory, light emitted by atoms originates from
transitions of electrons between electron levels of the same atom.
63- What does the word "seeing" mean to an astronomer using a telescope?
twinkling and blurring of the image due to turbulence in the Earth's atmosphere
127- When an object is moving toward you, the visible light it emits is Doppler-shifted toward the
ultraviolet.
116- What is a neutron?
uncharged particle similar in mass to a proton
15- One difference between violet light and red light is that
violet light has a shorter wavelength than red light.
24- The two ranges of electromagnetic radiation for which the Earth's atmosphere is reasonably transparent are
visible and radio radiation.
71- The main absorber in the atmosphere for infrared radiation, which impedes observations of astronomical infrared objects, is
water vapor, H2O.
126- When electromagnetic radiation (e.g., light) is Doppler-shifted by motion of the source away from the detector, the measured
wavelength is longer than the emitted wavelength.
97- Why does the Sun look red when it is setting?
Earth's atmosphere scatters shorter wavelength light more easily than longer, so more red light is left to reach our eyes.
76- Gamma rays are generally absorbed in the Earth's atmosphere. However, it is possible to build Earth-based observatories that detect secondary effects of gamma rays, such as the blue light produced when the particles they collide with move faster than the speed of light in air. This blue light is called
Cherenkov light.
54- What causes chromatic aberration in the objective lens of a telescope?
Different colors are refracted through different angles at each surface of the lens.
79- The temperature scale most often used by scientists is the
Kelvin scale
55- What is chromatic aberration in a telescope?
Light of different colors comes to a focus at different points behind the objective lens inside the telescope.
75- What technique is necessary to produce a telescope for focusing X rays from astronomical sources?
The X rays must be reflected at grazing incidence to the mirror surface; otherwise they will simply pass straight through the mirror.
98- Why is the sky blue?
The air molecules scatter blue light better than red light, so more blue light reaches our eyes.
18- If two photons in a vacuum have different energies, what can we say about the wavelengths of the photons?
The higher-energy photon has the shorter wavelength.
78- What changes would you expect to see in the resulting spectrum of emitted light from a piece of metal when it is heated slowly in an intense flame from 500 K to 1500 K?
The intensity of radiation would increase greatly, and the color would change from red through white to blue.
43- Which way does a light ray bend when it crosses the plane smooth surface of a dense transparent material (from air or a vacuum) at an angle to the perpendicular?
The light ray bends toward the perpendicular.
60- What is the purpose of the glass corrector plate at the front of a Schmidt telescope?
The plate corrects for spherical aberration in the primary mirror.
82- A scientist reports that his measurement of the temperature of the surface of a newly discovered planet is -20 K. What conclusion can you draw from this report?
The result is erroneous because absolute temperature cannot be negative.
45- How does the speed of light in a substance such as glass compare to the speed of light in a vacuum?
The speed of light in glass is slower than the speed of light in a vacuum.
9- What is the one fundamental difference between X rays and radio waves?
The wavelengths of X rays and radio waves are very different.
7- What is the relationship between color and wavelength for light?
Wavelength increases from violet to red.
103- The dark absorption lines in the solar spectrum are caused by
a cooler layer of gas overlying the hot solar surface, which contains many elements, including hydrogen, helium, magnesium, calcium, and iron.
36- The light-gathering power of a telescope depends directly on the
area of its primary mirror or lens.
25- An electromagnetic wave has a wavelength of 80 cm. This wave is
a radio wave.
67- One technique that astronomers are now using to increase the amount of detail that can be recorded with telescopes is
adaptive optics, where the tilt and shape of mirrors in the telescope are changed many times per second to compensate for atmospheric turbulence.
62- The major cause of blurred and unsharp images of objects observed through very large telescopes at the extreme limit of magnification is the
air turbulence in the Earth's atmosphere.
114- Ionization of an atom occurs when
an electron is removed from the atom.
