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Unformatted text preview: – HW1 – Tsoi – 1 This print-out should have 22 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Why do clothes often cling together after tum- bling in a clothes dryer? 1. air pressure 2. The dryer heat caused some of the fabrics to melt together. 3. electrical force correct 4. The clothes are electrically neutral. 5. gravitational force Explanation: Because the positively charged particles or negatively charged particles move from one article of clothing to the other, the clothing is not electrically neutral. 002 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 discharge the automobile correct 3. To warn the drivers 4. To transfer positive particles to the auto- mobile 5. To count the vehicles Explanation: Metal wire can conduct net charges to the ground so that it can make the automobile uncharged. 003 10.0 points In a crystal of salt there are electrons and positive ions. How does the net charge of the electrons compare with the net charge of the ions? 1. The net charge of the negative electrons is greater than the net charge of the ions. 2. Unable to determine 3. The net charge of the negative electrons is less than the net charge of the ions. 4. Sometimes the net charge of the negative electrons is greater than the net charge of the ions and sometimes it is less. 5. The net charge of the negative electrons has the same magnitude as the net charge of the ions. correct Explanation: The crystal as a whole has a zero net charge, so any negative charge in one part is countered with the same amount of positive charge in another part. Therefore the net charge of the negative electrons has the same magnitude as the net charge of the ions. 004 10.0 points The five thousand billion freely moving elec- trons in a penny repel one another. Why don’t they fly off the penny? 1. The shell of the penny prevents the elec- trons from flying. 2. They don’t have enough speed. 3. They are attracted to the five thou- sand billion positively charged protons in the atomic nuclei of atoms in the penny. correct 4. They cause a jam when they try to fly away. 5. The electrons attract each other. Explanation: The electrons are bound to the nuclei. – HW1 – Tsoi – (60250) 2 005 10.0 points How can a charged atom (an ion) attract a neutral atom? 1. The charged atom can hit the neutral atom and make it positively charged or nega- tively charged. 2. 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 3. The charged atom can produce secondary electrons to interact with the neutral atom and make it positively charged or negatively...
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This note was uploaded on 09/09/2008 for the course PHY 303L taught by Professor Turner during the Fall '08 term at University of Texas.
- Fall '08