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Physics 2

# Physics 2 - gilvin(jg47854 1 Coulombs Law meyers(21235 This...

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gilvin (jg47854) – 1: Coulomb’s Law – meyers – (21235) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This homework is due Tuesday, January 25, at midnight Tucson time. 001 10.0points You have a neutral balloon. The charge of an electron is 1 . 6 × 10 19 C. What is its charge after 12000 electrons have been removed from it? Correct answer: 1 . 92 × 10 9 μ C. Explanation: Let : n = 12000 and q e = 1 . 6 × 10 19 C . The removal of n electrons leaves a positive charge on the balloon of q = n × q e = (12000) ( 1 . 6 × 10 19 C) × 1 × 10 6 μ C 1 C = 1 . 92 × 10 9 μ C . 002(part1of2)10.0points A strong lightning bolt transfers about 25 . 1 C to Earth. How many electrons are transferred? The charge on an electron is 1 . 60218 × 10 19 C. Correct answer: 1 . 56662 × 10 20 . Explanation: Let : q = 25 . 1 C and q e = 1 . 60218 × 10 19 C . The charge is proportional to the number of electrons, so q = n | q e | n = q | q e | = 25 . 1 C |− 1 . 60218 × 10 19 C | = 1 . 56662 × 10 20 . 003(part2of2)10.0points The lightning bolt discharge lasts one mil- lisecond. What is the average current flowing from the cloud to ground? Correct answer: 25100 A. Explanation: Let : t = 1 ms = 0 . 001 s . I = q t = 25 . 1 C 0 . 001 s = 25100 A . 004 10.0points Imagine a charge in the middle between two parallel plate conductors. There is no net charge on the plates, and the plates are not connected to ground. q What will happen if the charge is moved a little away from the middle? 1. The charge will move away from the mid- dle. correct 2. The charge will remain stationary. 3. All of these can happen, depending on the size of the charge. 4. The charge will return to the middle. 5. There is not enough information to tell. Explanation: There will be an image-charge attracting it towards each metal surface. The charge will move towards the plate closest to it because the image-charge attracting it will be closest and thus stronger.

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gilvin (jg47854) – 1: Coulomb’s Law – meyers – (21235) 2 Any charge (free to move) will go toward the closest conductor it can find. 005 10.0points Two charges q 1 and q 2 are separated by a distance d and exert a force F on each other. What is the new force F , if charge 1 is increased to q 1 = 5 q 1 , charge 2 is decreased to q 2 = q 2 / 2, and the distance is decreased to d = d/ 2? Choose one 1. F = 25 / 2 F 2. F = 25 F 3. F = 10 F correct 4. F = 100 F 5. F = 5 / 4 F 6. F = 20 F 7. F = 50 F 8. F = 25 / 4 F 9. F = 5 F 10. F = 5 / 2 F Explanation: F = k q 1 q 2 r 2 = k (5 q 1 ) parenleftBig q 2 2 parenrightBig parenleftbigg d 2 parenrightbigg 2 = 10 k q 1 q 2 d 2 = 10 F F = 10 F .
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