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Astronomy 104, Spring 2016 Test 3 CORRECT SOLUTIONS ___________________________________________
Make sure your scantron has your name and code on it. Show a picture ID, and turn in the test paper with the scantron. It is advisable but not required to fill in the answers on the test paper.
There were many scrambled versions. Here is a solved copy of one of the versions. 1 2 3
Depends on the version. Depends on the version. Depends on the version.
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C
An atom has … types of main consRtuents, and these are … A: 3: protons, electrons, and neutrons B: 4. electrons, positrons, protons, and neutrons. C: 2: a nucleus and electrons D: 4: nuclei, protons, electrons, and neutrons. E: 5. electrons, positrons, protons, neutrons and neutrinos.
E
At what temperature will all molecules desintegrate? A: Above ~ 1 million K B: Above ~ 273 K C: Above ~ 100 K D: Above ~ 10,000 K. E: Above ~ 2000 K
A
B
Microwaves have no effect on living bodies (except general heaRng) because … A: each photon's energy is very small and only one interacts at a Gme. B: microwaves have too liIle total energy. C: But they do: they destroy DNA. D: But they do: they are poisonous. E: microwaves pass though living bodies without interacGon. A hydrogen nucleus is the same thing as … A: A proton and a neutron bound together. B: A proton. C: Hydrogen does not have a nucleus because it has no neutrons. D: Hydrogen does not have a nucleus because it is gas. E: An electron.
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B
A rotaRng star's spectum has A: no spectral lines. B: broadened spectral lines. C: redshiLed spectral lines. D: emission lines. E: blueshiLed spectral lines.
E
Can a chemical process turn hydrogen into helium? A: Yes, and that is the process that keeps the Sun hot. B: No, because helium has more charge than hydrogen. C: No, because a chemical process can turn hydrogen only into oxygen. D: Yes, but only at very hot temperature. E: No, because too much energy is needed to change one nucleus into another.
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B
Earth contains ~20% oxygen in its rocky BODY. (Not the atmosphere!) How much did it contain 4 billion years ago? A: ~ 80%. Burning processes have turned it into carbon and silicon since. B: ~ 50%. Pit of this, about 30% was turned into other types of atoms. C: None. Oxygen was made inside Earth out of silicon in the heat of the core of Earth. D: ~20%. Oxygen atoms do not change into different atoms. E: None. Oxygen was made out of carbon by plants and then absorbed into the ground. How was the speed of light measured for the first Rme? A: By measureing the slowing down of the Gme in a spaceship. B: Measuring the delay in the eclipses of Jupiter's moons. C: GeZng a laser reflecGon from the Moon. D: By measuring the delay in conversaGons of astronauts. E: By direct measurement in a laboratory experiment.
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How does the Doppler-‐effect affect the spectrum of a star? A: The star's light is stronger when the star is approaching us, and weaker when it is receding. B: The spectral lines of an approaching star are shiLed from the red end of the spectrum to the blue end. C: Spectral lines shiL (usually a Gny bit) when the star moves towards or away from us. D: An approaching star's light arrive to Earth sooner, which causes its spectral lines broaden. E: The color of a moving star looks redder/bluer than normal. How does the speed of light relate to the speed of radio waves and the speed of sound? A: Radio waves are fastest, light is middle, sound is slowest. B: They all have the same speed. C: Radio waves and light have the same speed, sound is much slower. D: Radio waves and sound are slow, light is fast. E: Sound and radio waves have the same speed, the speed of light is infinitely fast. How far is a star whose absolute brightness equals its apparent brightness? A: 1 pc. B: 100,000 light years C: 10 parsecs. D: 1 AU. E: 14 billion light years. How is blue different from red? A: Shorter wavelength. B: Longer wavelength. C: Red light travels faster than red. D: Blue light travels faster than red. E: Blue is pure color, red is a mix.
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A
How large is the Doppler effect in astronomy in pracRce? A: A Gny (say, 0.01%) shiL in the wavelength of spectral lines. B: A large shiL in the overall color of a star, say, from blue to red appearence. C: Both the posiGon of the spectral lines and the overall color of the star changes noGceably. D: It is impossble to detect the Doppler effect in the spectra of individual stars. E: A large shiL (say, 10%) in the wavelength of spectral lines.
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How long would it take a radio signal to reach the closest star? A: They would reach instantenously. B: 4.6 billion years. C: 2 hours. D: 4 years. E: 100 billion light years.
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Ionized hydrogen consists of … A: hydrogen molecules and metals. B: hydrogen molecules and salts. C: protons and electrons. D: single hydrogen atoms. E: hydrogen molecules.
B
Relate the energy of a blue photon to the energy of a red photon. A: Blue photons have a hundred Gmes as much energy as red photons. B: Blue photons have twice as much energy as red photons. C: Cannot tell: the energy of photons depends on the strength of the light. D: Blue photons have a hundred Gmes less energy than red photons. E: Blue photons have half the energy of red photons.
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The solar spectrum is a(n) … A: conGnuous spectrum. B: blueshiLed spectrum. C: absorpGon spectrum. D: redshiLed spectrum. E: emission spectrum.
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The spectral type of the Sun is A: G B: A C: K D: M E: B
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The wavelength of light determines its … A: speed. B: raGo of electric / magneGc field strength. C: intensity. D: color. E: polarizaGon.
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What can excite a hydrogen atom? A: UV radiaGon. B: A magneGc field. C: HeaGng to 1200 K. D: Red light. E: Infrared radiaGon.
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What can you tell from the wavelength of a spectral line? A: The temperature of the gas that emits the light. B: Which atom/molecule produced the line. C: How far is the source from the observer. D: The strength of gravity of the source object. E: The atmospheric pressure in the source object.
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What does ionizaRon mean? A: Electrons moving to a higher orbit in an atom. B: A chemical reacGon with an ionizing salt. C: Mixing interstellar gas with Fe-‐containing dust. D: Atoms losing (some of) their electrons. E: The breakup of molecules into atoms. What does the word 'burning' mean, scienRfically, when used for an everyday-‐life process? A: A nuclear reacGon in which atoms break up. B: Burning is the formaGon of water out of carbon dioxide. C: A nuclear reacGon in which atomic nuclei split. D: A chemical fusion with oxygen. E: The release of large amounts of energy into the air is called burning.
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What happens to maaer at 3000 -‐ 4000 degrees? A: Atomic nuclei change into each other. B: Atoms break up. C: All substances become solid. D: Atoms become ionized. E: Molecules break up.
B
What is absorbRon spectrum? A: When all colors of the rainbow are present in the spectrum. B: A few dark spectral lines on the background of a conGnuous spectrum. C: A few bright spectral lines on a black background. D: When a large range of wavelengths is missing in the spectrum. E: When all colors are blocked except a few bright lines.
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What is plasma? A: A viscous liquid. B: Gas that contains no free electrons. C: Hot gas with most molecules broken up into atoms. D: Gas that contains no electrons. E: (At least parGally) ionized gas.
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What makes a planetary nebula glow? A: Fluorescence due to the UV radiaGon of the hot central star. B: The reflected light of the hot central star. C: Sunshine reflected from the atmosphere of a planet. D: The reflected light of a low-‐temperature star. E: Dust parGcles radiate in infrared because they are hot.
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What type of spectrum does fluorescence produce? A: ConGnous spectrum. B: Emission spectrum. C: AbsorpGon spectrum. D: Distorted spectrum. E: Band spectrum.
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When cold(er) gas is located in front of a star, the spectrum will contain … A: a strong red conGnuum B: emission lines C: broadened spectral lines D: a strong blue conGnuum E: absorpGon lines.
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Which is the farthest object we can get a radar echo from? A: Neptune. B: the Moon. C: the closest cluster of galaxies. D: several of the closest stars. E: the Andromeda Galaxy.
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Which one is an example of the Doppler-‐effect? A: MagneGc fields make spectral lines break up into several lines. B: The moGon of a star makes spectral lines broaden. C: The overall color of a moving star changes. D: Gas illuminated by UV radiaGon glows in an emission spectrum. E: The spectral lines of a moving star are shiLed.
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Why did alchemists all fail? A: Because they did not know how to use electricity. B: Because they confused chemical elements with compounds. C: Because their substances were not sufficiently clean. D: Because atomic nuclei cannot be changed by chemical means. E: Because they did not have the necessary compuGng power to check their theories. A binary star system has a revoluRon period of 1 day. It is most probably a … A: telescopic binary. B: spectroscopic binary. C: a double star system without observable moGon. D: a system very close to the Sun. E: a system of two red giants.
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Compare a red star to a blue star. Surely, … A: the red star is younger. B: the red star is more massive. C: the red star is hoIer. D: the blue star is hoIer. E: the red star is older.
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How do we measure the mass of stars? A: We measure the strength of their magneGc field. B: Using Wien's law, applied to the color of the star. C: Using Kepler's II law applied on their planets. D: We measure how strong a gravitaGonal effect they have on the moGon of Earth. E: Using Kepler's III law for binary stars.
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How easy is it to measure stellar parallax with, say, high-‐quality amateur equipment? A: Even professional instruments cannot detect parallax. It exists only in theory. B: Very difficult but barely possible. C: Parallax is detectable even without instruments. D: It is very easy. E: It is impossible. Stars differ hugely in ____ but not so much in _______ .
A: size; brightness. B: mass; brightness. C: brightness; mass. D: brightness; size. E: mass; temperature. C
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Strong ultraviolet radiaRon comes only from stars of spectral type …, and why? A: All spectral types, because UV producGon does not depend on temperature. B: None, because stars do not radiate in UV. C: O & B, because these are hot enough. D: K & M, because these are hot enough. E: All spectral types, because they are all hot. The center of the Galaxy is 8 kpc away (1kpc=1,000 pc). How large is the parallax of a star that is located there? (Round.) A: ~ 0.001 as. B: ~ 0.2 million years. C: ~ 3 billion light years. D: 1.2 billion kilometers. E: 3 arc minutes.
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The spectral type of a star is related to … A: its chemical composiGon. B: its speed of moGon. C: its distance. D: the temperature in its core. E: its surface temperture.
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What does Stefan-‐Boltzman's law say? A: Each absorpGon line is brightest at a parGcular temperature. B: The temperature of a star is inversely proporGonal to the wavelength of its color. C: The power radiated by a surface element of a glowing body is proporGonal to the 4th power of its temperature. D: The absolute magnitude of a star is independent of its distance. E: The speed of rotaGon of a star is inversely proporGal to its temperature.
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What does Wien's law say? A: The wavelength of the light of an approaching body is shiLed towards blue. B: Warmer material absorbs red light stronger. C: Thermal glow gets of shorter wavelength when the temperature of the body is increased. D: HoIer objects appear redder (I.e. radiate in longer wavelength). E: HoIer gas radiates stronger than cold, proporGonally to the fourth power of temperture.
C
What is 1 parsec? A: The diameter of the Galaxy. B: The distance light travels in a year. C: The distance of a star with 1 as parallax. D: The Gme light takes to travel from the Sun to Earth. E: A unit of velocity, equals to the speed of light.
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What is a double-‐line binary star? A: A double star with a strong magneGc field. B: A doule star system with strong stellar wind. C: A star that is visibly broken up into a pair in the telescope and the orbital moGon is noGceable. D: A short-‐period binary with both stars' spectral lines visible. E: A star that is visibly broken up into a pair in the telescope but the orbital moGon is not noGceable.
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What spectral type is the red giant Betelgeuse? A: G. B: He. C: M. D: C. E: Hydrogen.
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The locaRon of a star on the main sequence is determined by its … A: orientaGon of the axis of rotaGon. B: age. C: mass. D: chemical composiGon. E: rate of rotaGon.
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What can you read off the HRD of a star cluster? A: Its mass. B: The number of stars in the cluster. C: Its age. D: Its distance. E: Its chemical composiGon.
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What is the simplest way to determine the distance to a far-‐away main sequence star? A: Using the HRD to find its color, then comparing it to its temperature. B: The HRD has parallax on the verGcal axis, so the color of the star can be used to tell the distance. C: Measuring the Gme light takes to arrive from the star. D: Using the HRD to find its absolute magnitude, and comparing to its apparent magnitude. E: Measuring its parallax. The reciprocal of parallax is the distance in parsecs.
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What makes the stars on the main sequence different from all the others? A: They are all very young. B: They produce energy while all the other stars do not. C: They are all very old. D: They were born from gas that contained a large amount of metals. E: Their energy source is hydrogen to helium fusion.
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What two things are related by the Hertzsprung-‐Russel diagram (HRD)? A: Spectral type and temperature. B: Mass and luminosity. C: Absolute magnitude and luminosity. D: Distance and apparent magnitude. E: Absolute magnitude and spectral type.
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Where is a red giant on the HRD? A: on the main sequence. B: up leL. C: up right. D: down right. E: down leL.
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How long would (chemical) burning be able to maintain the energy of the Sun? A: 1 year. B: A few hundred years. C: 6000 years. D: A million years. E: 10 billion hears. ProducRon, out of nucleus X, of nuclei other than X cannot produce energy. What is X? A: Fe. B: He. C: H. D: U. E: C.
B
What is the energy source of white dwarfs? A: Helium to carbon fusion. B: They have none, they are only slowly cooling off. C: RadioacGve decays. D: Burning hydrogen. E: Hydrogen to helium fusion.
B
What minimum temperature is needed for hydrogen to helium fusion? A: 3 K. B: 1 million K. C: 6000 K. D: 400 K. E: 200 million K.
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Which of the following uses the same physical process as the Sun to generate heat? A: A car engine. B: A hydrogen bomb. C: A nuclear reactor. D: A gas stove. E: An atomic bomb.
B
The central star of a planetary nebula is … A: A red giant. B: A white dwarf. C: A main sequence star. D: A brown dwarf. E: A supernova.
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All stars start their life … A: as giants. B: as dwarfs. C: on the main sequence. D: as red giants. E: as white dwarfs.
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How will the Sun end its life? A: As a white dwarf. B: Nothing will remain. C: As a black hole. D: As a planet. E: As a supernova.
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What determines what sort of an object remains aier a dead star? A: The planet system of the star. B: The chemical composiGon of the star. C: The age when the star collides with another one. D: The metallicity of the star. E: The star's mass.
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What stars become planetary nebulae? A: Only some double stars. B: None. Planetary nebulae are gas clouds and have nothing to do with stars. C: Those lighter than 1.44 solar masses. D: Those heavier than 1.44 solar masses. E: All.
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What stars blow up as supernovae? A: All white dwarfs. B: All. C: All red giants. D: Those similar to the Sun in mass, brightness and chemical composiGon. E: Those that are heavier than 1.4 solar masses at the end of their lives.
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When does a star become a red giant? A: When it collides with a black hole. B: When it exhausts all its fuel. C: In the beginning of its life. D: When it exhausts it hydrogen. E: When its core collapses into a supernova.
E
Where was the copper we find on earth manufactured? A: In a main sequence star. B: In a red giant. C: In interstellar space. D: In the hot core of Earth. E: In an exploding supernova.
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Where were the oxygen atoms of our atmosphere manufactured? A: In the oceans. B: In a supernova. C: In Earth's atmosphere. D: Underground inside Earth. E: In a red giant.
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Which star lives longer, one with a small or a large mass? A: The one with a small mass, because it contains more hydrogen. B: Equal: heavy stars have more fuel but use it faster in proporGon. C: The one with a small mass, because it is much dimmer. D: The one with a large mass, because it is hoIer. E: The one with a large mass, because it contains more hydrogen.
B
Will the Sun explode as a supernova? A: No, because only double stars become supernovae. B: No, it is not heavy enough for that. C: Yes, when it builds up iron in its core. D: Yes, when it exhausts its helium. E: Yes, when it uses up all its hydrogen.
