Exam 1 practice problems - Exam#1 practice problems 1 Have...

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Exam #1 practice problems Physics 227 1. Have a look at the situation shown. A soda can is resting on a plastic stand. A piece of aluminum foil hangs vertically from a thread (an insulator) so it is touching the right side of the soda can. A glass sphere that has been rubbed with silk (so it becomes positive) is slowly moved closer to the left side of the can, eventually touching it briefly. It is then slowly moved away. a. Describe what, if anything, happens to the glass sphere, the soda can, and the aluminum foil throughout this entire situation. Give any explanation for what happens (or why nothing happens). b. Repeat part a., except with the soda can replaced with a plastic bottle. 2. By accelerating electrons to extremely high speeds and firing them at nuclei we can probe the structure of the nucleus. By doing this particle physicists have determined that the radius of the proton is approximately 15 1.2 10 m . This is much smaller than the radius of an atom, which for hydrogen anyway, is approximately 11 5.3 10 m . Using this information, it’s possible to construct the following model of the hydrogen atom: The nucleus is a single proton which is going to be treated as a solid sphere of uniformly distributed positive charge with the radius stated above and total charge equal to the standard proton charge. The electron is not going to be treated as a particle. Instead it is going to be treated as an extended object, a thin spherical shell centered on the nucleus. It has the atomic radius stated above and total charge equal to the standard electron charge. a. What is the electric field outside of the atom as a function of distance ( r ) from the center of the nucleus. Explain your reasoning. Express your answer for all parts of this problem in terms of the charge on the proton ( e ), the radius of the nucleus ( 0 r ), and any other fundamental constants you need. b. What is the electric field between the nucleus and the electron shell as a function of distance ( r ) from the center of the nucleus. Explain your reasoning. c. What is the electric field within the nucleus as a function of distance ( r ) from its center? 3. Give detailed explanations for why the following happens. Draw charge diagrams to illustrate your explanations. a. A metal spoon is placed on a Styrofoam plate. Several tiny bits of aluminum foil are placed into the bowl of the spoon. A glass rod is rubbed with silk (to make the rod positive). Everything else is initially neutral. The rod is then touched to the end of the handle of the spoon. At the instant this happens, the aluminum foil bits fly out of the spoon. b. Another metal spoon is placed on another Styrofoam plate. Several new bits of aluminum foil are placed into the bowl of this second spoon. The glass rod is rubbed with silk again (to insure the rod is still positive). Again, everything else is initially neutral. This time, the rod is brought near the aluminum foil bits from directly above.
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This note was uploaded on 03/18/2012 for the course 12312 12312 taught by Professor 3123 during the Spring '12 term at Antioch University New England.

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Exam 1 practice problems - Exam#1 practice problems 1 Have...

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