Briefly explain your choice.

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1 Section I: Please answer all the questions in this section. If you like, you can always explain your answer, even on multiple-choice questions. I'll take the explanation into account and possibly give partial credit if your answer was wrong (or extra credit if your explanation was particularly insightful.) Question #1: You drop a brick from a roof. Which of the following is the best description of the energy exchanges as the brick falls? (You may assume that air resistance has very little effect on the fall.) a) The brick is gaining thermal energy, and losing kinetic energy. a) The brick is gaining electrical energy, and losing chemical energy. a) The brick is gaining kinetic energy, and losing gravitational potential energy. a) The brick is gaining both kinetic energy and gravitational potential energy; no energy is being lost e) The brick is gaining thermal energy, and losing kinetic energy. f) All forms of energy possessed by the brick are remaining exactly the same. Question #2: In Question #1, only one of the answers was the best description of what the falling brick is doing. But most of them still described process that could, in theory, happen to an object. Which one answer could NEVER happen to ANY object? Briefly explain your choice. Question #3: In J.J. Thomson's experiment with Cathode Ray Tubes, he sent a beam of fast-moving electrons between two charged metal plates. Which of the following diagrams best describes the trajectory that the electrons would take? a) The electrons passed between the plates in a almost perfectly straight line. b) The electrons orbited in circles between the plates. c) The electrons deflected noticeably toward the positive plate. d) The electrons deflected noticeably toward the negative plate. e) Some of the electrons ricocheted back sharply. f) No electrons were detected; this experiment proved that electrons do not exist. Question #4: What is the significance of the choice you picked in Question #3? (What did it teach Thomson about electrons?) Question #5: What if Thomson had managed to do his experiment with a beam of alpha particles, rather than a beam of electrons? Which of the trajectories shown in Question #3 would the alpha particles follow, and why?

2 Question #6: J.J. Thomson performed his cathode-ray experiments in the 1890s. Which of the following was NOT one of his discoveries? a) Particles smaller than atoms exist. a) An electron are both a particle and a wave. c) An electron carries negative charge. d) An electron's mass is tiny, (thousands of times less massive than a whole atom.) e) All electrons are identical to one another, no matter which type of atom they come from. Question #7: Which of the following was NOT one of Marie or Pierre Curie's discoveries? a) Light consists of individual "particles" of energy, called photons. b) The energy in radioactive decay comes from inside the atom itself. c) When an atom undergoes radioactive decay, it can emit millions of times more energy than it would when it forms a chemical bond. d) Discovered and named several new elements on the Periodic Table. e) Alpha decay happens only to elements with very high atomic numbers (around the mid-80s or above). Question #8: Which of the following was NOT one of Ernest Rutherford's discoveries? a) Almost all its mass of an atom is concentrated in a tiny speck called the nucleus. b) The nucleus is positively charged. c) The nucleus contains smaller particles called protons. d) An "alpha particle" is actually a helium nucleus. e) Energy cannot be created or destroyed. Question #9: Suppose you are trying to repeat the early experiments on the "photoelectric effect": that is, you are trying to use light waves to knock electrons out of a sheet of metal. You shine a very bright green light on the metal sheet, but according to your instruments, no electrons are knocked free. If you want to liberate electrons, which of the following changes to your experiment might help? a) Use an even brighter green light. b) Use a dimmer green light, c) Use a higher-frequency light. d) Use a lower0frequency light. e) Use both sound waves and light waves. Briefly explain why you chose the option you did.

3 Question #10: If you make the change you describe in Question #9,the light source you use may appear visibly different to your eyes. Describe the sort of change that might take place. Question #11: Rank the following five "particles" in order, from the one with lowest energy to the one with highest energy: a) A single ulltraviolet photon. b) A single radio-wave photon. c) A single photon of blue light. d) A single photon of red light. e) A single gamma-ray photon. Lowest Energy > Highest Energy Question #12: An element's "atomic number" on the periodic table -- hydrogen is element #1, carbon is #6, uranium is #92, etc. -- indicates which of the following properties? a) The number of protons in the nucleus. b) The number of neutrons in the nucleus. c) The historical order in which the element was discovered. d) The mass of the atom. e) The amount of energy released when the atom forms a chemical bond. Question #13: In the famous experiment in which Rutherford and his team discovered protons, they bombarded nitrogen nuclei (element #7) with fast-moving alpha particles (which are actually helium nuclei, element #2.) Why was it so important that the alpha particles be fast-moving? Why could Rutherford NOT easily repeat this experiment using higher-atomic-number elements, such as aluminum (Element #13) as the "targets" for the alpha particles?

4 Question #14: Niels Bohr's model of the hydrogen atom was an early (and in retrospect, primitive) step toward understanding quantum mechanics. For each of the following sentences, label them as: A: This was a feature of Bohr's model which turned out to be correct, or close to correct. B: This was a feature of Bohr's model which turned out to be wrong. C: This was not a feature of Bohr's model at all. Atoms are tiny, indivisible spheres. Electrons within an atom have specific allowed energy levels. Electrons orbit the nucleus on perfectly circular trajectories. When an electron jumps from a higher energy level to a lower one, it emits a photon. Atoms consist of a sphere of positively-charged "gelatin", with electrons floating freely in it. Planck's constant (h or hbar) plays an important role in the model.

5 Section II: Long-Answer Problems On the attached blank sheets, please answer at least TWO of the following problems. They will probably require at least a couple of solid paragraphs to answer fully; if you have less than that to say, then either you are admirably concise, or you might want to choose a different topic. Topic #1: Describe what is meant by the "plum pudding" model of the atom. What evidence led us to adopt this model? What was at least one important thing the model got right, and at least one important thing it got wrong? What evidence eventually led us to replace the model with a better one? Topic #2: We've discussed a number of scientists who made interesting and fundamental discoveries about nature: Emilie du Chatelet, Pierre & Marie Curie, Albert Einstein, Ernest Rutherford, Erwin Schrödinger, and many others. Choose one or more of these scientists, and discuss the importance of their accomplishments. What vital things did they discover? What misunderstandings about the universe did they help dispel, and what future discoveries would they make possible? Topic #3: The discovery of photons -- "particles" of light -- changed physics in profound ways. Two of the immediate puzzles it helped solve were the ultraviolet catastrophe and the photoelectric effect. Choose one (or both, if you like) of these two phenomena, and explain in detail how it supported the idea of photons. What situation was involved? What would we expect to happen if light was purely a wave? What actually happens? How does the phenomenon make more sense once we introduce the idea of photons? Topic #4: When Marie Curie learned of Henri Becquerel's discovery of "Uranium Rays" -- in other words, of the phenomenon of radioactivity -- she immediately believed it was the most fascinating mystery in all of physics. What makes radioactivity so remarkable, and how did it seem to defy everything people understood about atoms at the time? Topic #5: Many of Rutherford's famous experiments were intended to investigate one thing, and ended up proving something much more surprising (and often, much more important.) Two in particular that come to mind are the "gold foil" experiment, and the discovery of the proton. For one of these experiments, please describe what Rutherford and his team were expecting to find, and what surprising result they did find instead. What important physical properties of the atom were revealed? Topic #6: If you would rather write on a different topic than the ones listed thus far, come talk to me and suggest a topic that seems about the same complexity as the listed ones. I will almost certainly agree to your topic, though I might make a few suggestions on aspects of your topic to make sure to cover.