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Exam 2 Answers 1 Astronomy 101.003 Hour Exam 2 March 10, 2011 QUESTION 1: The half-life of Ra226 (radium) is 1600 years. If you started with a sample of 100 Ra226 atoms, approximately how many Ra226 atoms would be left 3200 years later? a) 200. b) 100. c) 50. d) 25. e) 0. QUESTION 2: Olber’s Paradox is related to: a) How can the Universe expand when there is nothing to expand into? b) How could the Universe have once fit into a single point? c) How can the speed of light not depend on the velocity of the source? d) Why does light bend in a gravitational field? e) Why is (most of) the sky dark? QUESTION 3: The most common element in the Universe is: a) Hydrogen. b) Helium. c) Carbon. d) Iron. e) Silicon. QUESTION 4: An isotropic universe is one which: a) Is expanding equally in all directions. b) Is the same everywhere. c) Started from a single point. d) Looks the same at all distances. e) Looks the same in all directions. QUESTION 5: Penzias and Wilson were studying microwave radiation from space because: a) They had a telescope that could do that and they wanted to use it. b) They were looking for the cosmic microwave background radiation. c) They were studying the effect of pigeon poop on antennae. d) They were studying the noise to be encountered when communicating with microwaves. e) They had nothing to do with studying microwave radiation from space. QUESTION 6: Properties of the cosmic microwave background radiation include: a) It follows a black body spectrum and it is nearly the same in all directions. b) It follows a black body spectrum and depends strongly on direction. c) It is nearly the same in all directions and it shows hydrogen emission lines. d) It shows hydrogen emission lines and it is nearly the same in all directions. e) It is isotropic random noise. QUESTION 7: Approximately when do scientists believe the universe began? a) 4047 BC. b) One billion years ago. c) 14 billion years ago. d) 62 billion years ago. e) It had no beginning. QUESTION 8: According to the Equivalence Principle, gravity is equivalent to: a) Curvature. b) Net force. c) Electric force. d) Acceleration. e) The state of free-fall. 2 QUESTION 9: In a curved space: a) The sum of the interior angles of a triangle = 180°. b) The shortest distance between two points is a straight line. c) Two parallel lines never meet. d) All of the above. e) None of the above. QUESTION 10: Airlines take great circle routes for long-distance travel because: a) It is the shortest route. b) It is the route that keeps the direction of travel constant. c) It minimizes the amount of time over water. d) It takes maximum advantage of the jet stream. e) Airlines do not take great circle routes. QUESTION 11: You are drugged and then awake in a closed room. You do not know where you are. You drop your flashlight and notice that it falls straight downward with an acceleration of 9.8 m/s2. This shows that you are: a) Stationary in a gravitational field. b) Stationary or moving with a constant velocity in a gravitational field. c) Accelerating upward at 9.8 m/s2. d) Accelerating downward at 9.8 m/s2. e) You could be accelerating upward or in a gravitational field or a combination of both. QUESTION 12: The Equivalence Principle is: a) Known to be true because it is a principle. b) Taken as true because Einstein proposed it. c) Just a scientific theory, capable of being proven wrong. d) Not a scientific theory because it involves thought experiments. e) Capable of being proven true. QUESTION 13: Hubble developed his famous law, using what information about galaxies? a) Distances and redshifts. b) Diameters and redshifts. c) Luminosities and redshifts. d) Shapes and redshifts. e) Velocities and redshifts. QUESTION 14: The distance to quasars are measured by: a) Observing Cepheid variable stars in them. b) Determining their redshifts. c) The Tully-Fisher relation. d) Parallax. e) Observing supernovae in them. QUESTION 15: If you measure the redshift of two distant galaxies and find that galaxy A is moving away from us at 15,000 km/s and galaxy B is moving away at 60,000 km/s, then you can conclude that: a) Galaxy A is twice as far away as galaxy B. b) Galaxy B is twice as far away as galaxy A. c) Galaxy A is four times farther away than galaxy B. d) Galaxy B is four times farther away than galaxy A. e) Galaxy A is less bright than galaxy B. QUESTION 16: Which of the following statements is true about virtually all galaxies compared to the Milky Way galaxy: a) They are older. b) They are larger. c) They are smaller. d) They are moving away from the Milky Way. e) They rotate slower. 3 QUESTION 17: What keeps light from escaping a black hole? a) A photon sphere that reflects all light. b) The event horizon, which is an opaque sphere. c) Gravity. d) An ultrastrong magnetic field. e) Nothing – light can escape from a black hole along the field lines. QUESTION 18: How can we detect a black hole? a) Gamma rays, being the most energetic type of electromagnetic radiation, will escape and can be detected. b) Observing the effects of the strong gravitational force on nearby objects. c) The gravitational force is equal to and opposite to the centrifugal force. d) It emits a black body spectrum. e) The gravitational force is equal to and opposite to the outward pressure. QUESTION 19: Because almost all galaxies are redshifted, we know that: a) We are near the center of the universe. b) There was no beginning of time. c) There is dark matter in the universe. d) There is dark energy and dark matter in the universe. e) The universe is expanding. QUESTION 20: Gravity waves: a) Are not believed to exist. b) Have been detected. c) Are so weak they can never be detected. d) Are very difficult to observe but are searches for them are underway. e) Are detected during earthquakes. QUESTION 21: How can the age of the universe be estimated from Hubble’s Law? a) From the velocity and distance to galaxies, we can estimate the time it took them to reach their present positions after the Big Bang. b) By seeing the most faraway galaxies, the distance in light-years tells us how old the universe is. c) From the distance and velocity of distant galaxies, we can estimate how much time was needed to accelerate them to their present velocities. d) By measuring how long it took the light to get to us from the edge of the universe. e) There is no way to do this. QUESTION 22: Which of the following is Hubble’s Law? a) The faster a galaxy spins, the larger it is. b) The greater the distance to a galaxy, the fainter it is. c) The greater the distance to a galaxy, the faster it is receding from us. d) The more distant a galaxy is from us, the younger it looks. e) The younger a galaxy appears, the higher its luminosity. QUESTION 23: Vesto Slipher found that the spectrum from the Andromeda nebula is blue-shifted. This means that: a) Andromeda is rotating rapidly. b) Andromeda is an active galaxy. c) Andromeda contains many young stars. d) Andromeda is moving away from us. e) Andromeda is moving towards us. QUESTION 24: Why do virtually all galaxies in the universe appear to be moving away from us? a) We are located near where the Big Bang occurred. b) We are located near the center of the universe. c) Observers in all galaxies see the same thing because of the expansion of the universe d) They aren’t moving away from us, we are moving away from them e) The statement is false: most galaxies do not appear to be moving away from us. 4 QUESTION 25: What is the origin of the Cosmic Microwave Background: a) Electromagnetic radiation remaining from the Big Bang. b) Dirt in microwave antennae. c) Quasars. d) Pulsars. e) Blackbody radiation from distant galaxy superclusters. QUESTION 26: The spectral shape of the cosmic microwave background radiation is: a) The sum of spectra for hydrogen and helium. b) The same as the spectrum of the Sun. c) A black body spectrum with a temperature of 2.7K. d) A flat spectrum. e) An absorption spectrum. QUESTION 27: How do gravitational lenses occur? a) Gravity curves space and light follows this curvature. b) Interstellar gas bends light like glass does. c) Light can be scattered by intense radiation from quasars. d) The cosmic microwave background radiation causes light to curve. e) It doesn’t occur, as gravitational lenses have not been observed. QUESTION 28: The existence of dark energy shows that: a) The Universe is expanding. b) There is unobserved mass in the Milky Way. c) Space is curved near a black hole. d) Gravitational waves exist. e) Hubble’s Law is not correct at large distances. QUESTION 29: Edwin Hubble’s discovery of a Cepheid variable in the Andromeda nebula showed that: a) The Andromeda nebula is not part of the Milky Way galaxy. b) The Andromeda nebula contains dark matter. c) The Andromeda nebula is red-shifted. d) The Andromeda nebula is moving towards us. e) The Universe is flat. QUESTION 30: A galaxy is at a distance of one billion light years.
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