Download here

PHYS 175 (2014) Mid-­‐‑term Examination Name: ____SOLUTION______ Lab Section: _______ 1. Which of the following would cause a scientific theory to be rejected? a) It does not agree with previous theories. b) It does not correctly predict experimental observations. c) Most scientists consider the theory to be wrong. d) The technology has not yet been developed to make the observations that would test the theory. 2. If the Earth’s axis were not tilted, a) a day and night would last 365 Earth days. b) the effect of seasons would be exaggerated. c) there would be no seasons. d) the Earth would always keep the same side facing toward the Sun. 3. Solar eclipses only occur when the phase of the Moon is a) new. b) full. c) first quarter. d) last quarter. 4. Kepler’s three laws a) were initially derived from fundamental physics laws. b) were initially found from observation and are empirical rules that describe how the planets move. c) were handed down from the ancient Greeks. d) are now known to be grossly incorrect. 5. Which of the following objects emits a continuous spectrum in which light is present at all wavelengths? a) The filament of a light bulb b) The low-­‐‑density neon gas in an overhead sign c) A single atom that emits light when an electron jumps from a higher state to a lower state d) Light from a low-­‐‑density nebula heated by a nearby star 6. The light-­‐‑gathering power of a 6-­‐‑m reflector is bigger than for a 2-­‐‑m reflector telescope by a factor of a) 3x. b) 4x. c) 6x. d) 9x. 7. The spectrum of light from Saturn’s satellite Titan is shown in this figure. Which absorption lines are due to chemicals in Titan’s atmosphere? a) H b) O2 c) CH4 d) All of the above 8. The extrasolar planets discovered so far tend to have a much higher mass than Earth, and many of them are Jupiter’s size. The reason for this is that a) extra-­‐‑solar Jupiter-­‐‑sized planets are much more abundant than Earth-­‐‑sized planets. b) astronomers are only interested in looking for really large planets. c) the methods of planet detection developed so far work best for very large planets. d) extra-­‐‑solar Jupiter-­‐‑sized planets are all really hot, and hot planets are easier to detect. 9. The Earth’s magnetic field is generated by a) electric currents in the liquid outer core; the field has never changed direction. b) electric currents in the liquid inner core; the field has never changed direction. c) electric currents in the liquid outer core; the field has reversed many times in the past. d) electric currents caused by interactions with the solar wind. 10. Which of the following is most likely responsible for the Moon’s formation? a) Asteroid debris from space was collected in Earth’s orbit, and this material slowly coalesced to form the Moon. b) A large body impacted the Earth during its early formation. The impact ejected material into space that later formed the Moon. c) The Moon is merely a large captured asteroid. d) The Moon split off from the Earth, leaving the Pacific Ocean basin behind. 11. Why is the surface of Mercury cooler than the surface of Venus? a) Mercury moves too rapidly around the Sun to be heated up significantly. b) Mercury, unlike Venus, does not have an atmosphere and there is no greenhouse effect. c) Mercury is much smaller than Venus. d) Mercury’s magnetic field deflects some solar radiation. 12. The rings of Saturn are mostly located within the Roche limit because a) particles outside the Roche limit can escape Saturn. b) any large solid object held together by gravity, such as a small moon, is torn apart by tidal forces if it is within the Roche limit. c) the strong gravity of Saturn has compressed the rings so that they are close to the planet. d) Saturn has a density less than water. 13. Enceladus, a smaller satellite of Saturn, is unusual in that a) its partially cratered surface suggests that it may be active. b) it underwent a large crater impact which probably came close to breaking the satellite into pieces. c) it has a strong magnetic field. d) it’s albedo is nearly mirror-­‐‑like, at ~0.99. 14. What evidence suggested that Pluto was an object in our solar system (and not a distant faint star) when it was first discovered? a) Telescopes showed it had a disc. b) Telescopes showed it had a moon. c) Its gravitational influence on Neptune showed that it was nearby. d) It moved against the background of stars indicating that it was probably nearby. 15. Galileo’s observation of the phases of Venus were a “nail in the coffin“ that disproved the theory of a) Kepler’s 3 Laws. b) Copernicus’ heliocentricism (a Sun-­‐‑centered solar system). c) the phases of the Moon. d) Ptolemy’s geocentricism and epicycles. 16. Isolated atoms, such as atoms in a low-­‐‑density gas cloud, only emit light at certain wavelengths. Why? a) They cannot be made hot enough to emit at all wavelengths. b) The electrons in the atom are allowed to have any energy. c) The electrons in the atom are allowed to have only certain energies. d) The atoms are isolated from one another. 17. As the solar nebula contracted, much of its material formed into a disk. This happened because a) the nebula was cool and so everything fell toward the center very rapidly. b) the nebula was spinning. c) the nebula always had a disk shape. d) Kepler’s laws did not hold in the early solar system. 18. Which of the following have not been found on Mars? a) Moving tectonic plates b) Wispy clouds c) Dust storms d) Advancing and receding polar icecaps 19. Jupiter radiates more energy into space than it receives from the Sun. What is the primary source of the excess energy that Jupiter radiates? a) Decay of radioactive materials in Jupiter'ʹs core b) Tidal forces from Jupiter'ʹs moons c) Jupiter is actually an infrared star, not a planet d) Jupiter is still contracting, and the contraction releases energy 20. Which of the following correctly identifies the characteristics of a terrestrial planet? a) Dense, made mostly of H and He, many rings and moons, no solid surface b) Dense, contains very little H and He, no rings and few moons, solid surface c) Dense, contains very little H and He, many rings and moons, no solid surface d) Less dense, made mostly of H and He, no rings and few moons, no solid surface 21. A blackbody a) absorbs all the light incident on it. b) reflects all the light incident on it. c) is a body at very low temperature. d) cannot emit any radiation whatsoever. 22. The Stefan-­‐‑Boltzman law for a blackbody states that the energy flux of reemitted radiation is proportional to the object’s temperature to the fourth power: F = σT4. Say a star (which is a pretty good approximation of a blackbody) increases its temperature by a factor of 3, by what factor will the energy flux increase? a) 3x b) 9x c) 12x d) 81x 23. If a planet’s orbital period P is given in years and its semimajor axis a in AU, Kepler’s Third Law reads as P2 = a3. Consider a small asteroid that takes eight years to orbit the Sun. What would its semimajor axis be? a) 64 AU b) 512 AU c) 4 AU d) 2.83 AU 24. An object is at 3000 K, emitting radiation that peaks at an infrared wavelength of around 1000 nm. Then the object is heated to 12,000 K and emits only a small fraction of its total energy at infrared wavelengths. At what temperature does the object emit more infrared radiation? Explain. (Hint: The figure below may help you answer the question.) A hotter object emits more radiation at all wavelengths than a cooler one. Even though the proportion of IR radiation is lower with the hotter object, it still emits more than the cooler object. So the 12,000 K object emits more IR radiation. 25. In a few sentences, describe why the study of astronomy has some benefit to society. There are many possibilities here, so I’ll list some in bullet form: -­‐‑ to learn about the origins of our planet, solar system, galaxy and the universe -­‐‑ to learn the fundamental laws of nature (this has led to many valuable applications of science) -­‐‑ in early times, it was important for agriculture and farming -­‐‑ to satisfy the human desire for exploration (in this case, space) -­‐‑ an excellent modern example is the Global Positioning System (GPS) -­‐‑ satellite communications came from space technologies -­‐‑ for pleasure, e.g. the enjoyment of learning, the artistic nature of astrophotography and imagery, or science fiction -­‐‑ EOS (NASA’s Earth Observing Satellites) for weather analysis on Earth -­‐‑ space weather observations from satellites (communications) -­‐‑ …