PHYS 160 Astronomy Test #2 Fall 2017 Version A

Transcription

1 PHYS 160 Astronomy Test #2 Fall 2017 Version A

2 I. True/False (1 point each) Circle the T if the statement is true, or F if the statement is false on your answer sheet. 1. A blackbody emits all of its radiation at a single wavelength or frequency. 2. Any telescope in space can measure both x-rays and visible wavelengths with the same optics (mirrors and lenses). 3. Hydrogen is the most abundant element in the universe. 4. It is possible to tell if an emission spectrum is produced by hydrogen atoms or helium atoms. 5. Sound waves are part of the electromagnetic spectrum. 6. The blackbody curve can tell us the temperature of the object at its surface. 7. The Hubble Space Telescope (HST) is the largest optical telescope ever built. 8. The number of protons in an atom determines the element it represents. 9. X-rays travel faster than yellow light. 10. As the frequency of light increases, the wavelength of light also increases. II. Definitions (1 point each). There are 10 definitions given. Select the word or phrase that best matches the definition from the table of words below. Put your answer on the answer sheet. Note, there are more words than there are definitions, so not all of them will be matched. Angstrom Wien s law parsec Cassegrain refraction wavelength focus proton frequency photon intensity nanometer electron Zeeman effect Newtonian telescope blackbody interferometry Absorption spectrum Emission spectrum Doppler shift reflection Stefan s law neutron spectroscopy Ground state 1. A hypothetical perfect radiator that absorbs and re-emits all radiation that falls upon it. 2. A splitting of spectral lines in the presence of a magnetic field. 3. A discrete unit of electromagnetic energy. A small packet of light x m. A small unit of distance, roughly equal to the size of a hydrogen atom. 5. An optical arrangement in a reflecting telescope in which light rays are reflected by a secondary mirror through a hole in the primary mirror. 6. The change in wavelength of radiation due to relative motion between the source and the observer along the line of sight. 7. A negatively charged subatomic particle usually found in orbit around the nucleus of an atom. 8. The number of waves that pass a point in space per unit of time. 9. The bending of light rays when they pass from one transparent medium to another. 10. The relationship that the dominant wavelength of radiation emitted by a blackbody varies inversely with its temperature.

3 III. Multiple Choice (1 point each) Select the letter next to the best answer for each question. Circle the letter on your answer sheet. 1. According to Wien's law, a hotter object will appear a cooler object. a. redder than b. bluer than c. blacker than d. the same color as 2. A cool, dilute gas between an observer and a continuous hot source will produce which of the following? a. The peak of the continuous spectrum would be shifted toward smaller wavelengths. b. Dark absorption lines.would appear in the spectrum. c. The spectral lines would be broadened by the heat from the source. d. The peak of the continuous spectrum would be shifted toward longer wavelengths. e. Bright emission lines would appear in the spectrum. 3. A Newtonian telescope uses a. only one mirror with its front surface shaped into a parabola b. one curved mirror and one flat mirror at a 45 degree angle to the first mirror axis c. two flat mirrors inclined to each other at a right angle d. two curved mirrors, one convex, the second concave in shape e. a series of lenses to focus and magnify the light 4. A photon can boost an electron in an atom to a larger orbit if a. it has exactly the amount of energy required b. it is moving in the right direction c. it has the proper speed d. none of the above; photons are produced by electrons, not absorbed by them 5. Arecibo telescope in Puerto Rico is a. A large, Earth-based optical telescope b. an orbiting optical telescope c. a single radio telescope d. an array of radio telescopes 6. Chromatic aberration occurs in a refracting telescope when a. the different colors of light do not focus at the same point. b. some wavelengths are scattered out of the telescope by imperfections in the glass c. light in the lense is reflected back by the front surface of the lens. d. the lenses bend under their own weight, distorting the final image. e. light from some wavelengths is absorbed by the lenses, distorting the colors of objects.

4 7. If you want to design a device that will detect animals at night by the radiation that they give off, even if the night is totally dark, to what wavelength range should you make the device sensitive? a. ultraviolet b. visible light c. no device can detect objects on a totally dark night d. the infrared 8. In light of the same color, each photon has the same a. wavelength b. energy c. frequency d. speed e. all of the above 9. In the Bohr model, light is emitted from an atom when a. an electron moves from an inner orbit to an outer orbit. b. an atom gains energy c. an electron moves from an outer orbit to an inner orbit. d. one element reacts with another e. Both A and B 10. Light waves of greater frequency have a. shorter wavelength. b. longer wavelength. c. either of the above; there is no direct connection between frequency and wavelength. d. higher speed e. smaller speed 11. Our sun emits its most intense radiation in which region of the electromagnetic spectrum a. infrared b. visible light c. ultraviolet d. x-rays 12. SOFIA is a new a. ground-based radio telespcope b. Infrared satellite orbitting Earth c. Infrared telescope mounted in a 747 jet airplane d. Visible wavelengh telescope mounted in a 747 jet airplane e. Visible wavelength telescope in space.

5 13. The biologically most damaging rays have a. the highest speed b. the longest wavelength c. the shortest wavelength d. the lowest frequency 14. The energy of a photon is indirectly proportional to the photon s a. speed b. wavelength c. frequency d. temperature e. brightness 15. The frequency at which a star emits the most light depends on the star s a. distance from us b. brightness c. temperature d. eccentricity e. velocity towards us or away from us 16. The Keck telescope is a. A large, Earth-based optical telescope b. an orbiting optical telescope c. a single radio telescope d. an array of radio telescopes 17. The main reason for placing a telescope and scientific equipment into an aircraft in order to carry out infrared astronomy is a. to obtain photographs of resolution higher than can be obtained on the ground. b. to avoid stray IR radiation from the warm Earth and its occupants. c. to avoid the absorption of the IR radiation by water vapor in the lower atmosphere. d. to obtain longer observing times on specific sources by moving in the direction of the Earth's rotation. 18. The parameter of an atom which defines its chemical properties is a. its temperature b. its size c. the number of protons in the nucleus d. the total number of protons and neutrons in the nucleus 19. The wavelength of visible light is a. millions of light years b. nearly one mile c. about an inch d. a tiny fraction of an inch

6 20. The process of combining the data from 2 or more telescopes to increase resolution is called a. Absorption b. digitization c. false color process d. interferometry e. spectroscopy 21. What effect will occur when we receive light from a source that is receding (moving away from) us at a high speed? a. absorption b. redshift c. blueshift d. blackbody radiation e. Stefan s Law 22. What is the one fundamental difference between X rays and radio waves? a. They always come from different sources. b. Their wavelengths are very different. c. Their speeds in outer space are different. d. Radio waves are always wavelike, whereas X rays always behave like particles. 23. What wavelength does the Chandra satellite explore? a. radio b. visible c. x-rays d. gamma e. infrared 24. Why are there blue-shifts rarely observed in galaxies? a. More energy is required to make a blue photon than a red one. b. Very few galaxies are moving toward us. c. Galaxies contain far more red stars than blue stars d. Most telescopes are ill-equipped to measure blue-shifts e. Blue light is more strongly absorbed than red light 25. What is the greatest obstacle to observing the universe in the infrared region of the spectrum from an observatory on the ground? a. The longer wavelengths of infrared radiation compared to those of visible light b. Seeing, i.e., the twinkling of objects seen through the Earth's atmosphere c. Water vapor in the Earth's atmosphere d. Too much heat from the Sun and ground

7 26. Visible light has a wavelength range of a. 400 to 700 nanometers b. 400 to 700 centimeters c. 400 to 700 meters d. 400 to 700 AUs 27. Most large observatories are built A close to populous areas for easy access B on desert mountains for clear weather and dark skies C in remote areas to keep tourists away D no choice 28. When light passes through a prism of glass, the a. different colors are caused by multiple reflections in the prism and interference between the resulting beams. b. prism absorbs colors from different parts of the broad beam coming out of the prism, leaving the complementary colors that we see. c. prism adds colors to different parts of the broadly scattered beam coming out of it. d. different colors or wavelengths of light are separated in angle by the prism. 29. The main reason for placing astronomical telescopes and detectors on satellites is to a. avoid dust and haze in Earth's atmosphere. b. avoid light pollution from cities and other built-up areas. c. get closer to the objects being viewed. d. get above the absorption in Earth's atmosphere. 30. Our present understanding of the nature of light is that it a. Behaves only as a wave b. Behaves only as a particle c. Displays behavior of both waves and particles d. Is completely different than both waves or particles

8 IV. Short Answer Questions Answer any five (5) of the following questions. Each question is worth 10 points. Answers may contain paragraphs, lists, and drawings. Please put your answers on the white paper provided. 1. Compare and contrast refractive and reflective telescopes. Which type is more commonly used in modern telescopes? Why? 2. List and briefly describe five kinds of information that can be gathered from spectral analysis of light from an object. 3. What is the Doppler shift? Explain how the doppler shift works for sound waves and give some every day examples. Why is the Doppler Shift important to astronomers? 4. Why do astronomers study light other than visible light? 5. Name and briefly describe 3 different large research telescopes on the surface of Earth. 6. Name and briefly describe 3 different space telescopes. 7. Compare an optical reflecting telescope to a radio telescope. What do they have in common? How are they different?