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Unformatted text preview: oliver (jmo673) HW01 Tsoi (59090) 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points At some automobile toll-collecting stations, a thin metal wire sticks up from the road and makes contact with cars before they reach the toll collector. What is the purpose of this wire? 1. To transfer electrons to the automobile 2. To transfer positive particles to the auto- mobile 3. To count the vehicles 4. To discharge the automobile correct 5. To warn the drivers Explanation: Metal wire can conduct net charges to the ground so that it can make the automobile uncharged. 002 10.0 points The five thousand billion freely moving elec- trons in a penny repel one another. Why dont they fly off the penny? 1. They are attracted to the five thou- sand billion positively charged protons in the atomic nuclei of atoms in the penny. correct 2. The shell of the penny prevents the elec- trons from flying. 3. The electrons attract each other. 4. They dont have enough speed. 5. They cause a jam when they try to fly away. Explanation: The electrons are bound to the nuclei. 003 10.0 points How does the magnitude of the electrical force between a pair of charged particles change when they are brought to half their original distance of separation? 1. doubles 2. Reduces to one half of original value 3. Doesnt change 4. quadruples correct 5. Reduces to one quarter of original value Explanation: By the inverse square law, at half the dis- tance the electric force field is four times as strong: F 1 ( 1 2 r ) 2 = 4 r 2 004 10.0 points How can a charged atom (an ion) attract a neutral atom? 1. The charged atom can produce secondary electrons to interact with the neutral atom and make it positively charged or negatively charged. 2. The charged atom can hit the neutral atom and make it positively charged or nega- tively charged. 3. The charged atom can emit x rays to induce ionization of the neutral atom. 4. An ion polarizes a nearby neutral atom, so that the part of the atom nearer to the ion acquires a charge opposite to the charge of the ion, and the part of the atom farther from the ion acquires a charge of the same sign as the ion. correct Explanation: An ion polarizes a nearby neutral atom, so that the part of the atom nearer to the ion acquires a charge opposite to the charge of oliver (jmo673) HW01 Tsoi (59090) 2 the ion, and the part of the atom farther from the ion acquires a charge of the same sign as the ion. 005 10.0 points An electron is released a short distance above Earths surface. A second electron directly below it exerts an electrostatic force on the first electron just great enough to cancel the gravitational force on it....
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- Fall '09