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Unformatted text preview: sicher (gns249) – H1ElFieldsDiscrete – Avram – (1956) 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 A plastic rod is rubbed against a wool shirt, thereby acquiring a charge of − 4 . 9 μ C. The charge on an electron is 1 . 6 × 10 − 19 C. How many electrons are transferred from the wool shirt to the plastic rod? Correct answer: 3 . 0625 × 10 13 . Explanation: Let : q = − 4 . 9 μ C = − 4 . 9 × 10 − 6 C and e = − 1 . 6 × 10 − 19 C . The total charge is q = n e e n e = q e = − 4 . 9 × 10 − 6 C − 1 . 6 × 10 − 19 C = 3 . 0625 × 10 13 . 002 10.0 points Two metal spheres that are initially un- charged are mounted on insulating stands, as shown. X Y − − − − A negatively charged rubber rod is brought close to but does not make contact with sphere X . Sphere Y is then brought close to X on the side opposite to the rubber rod. Y is allowed to touch X and then is removed some distance away. The rubber rod is then moved far away from X and Y . What are the final charges on the spheres? Sphere X Sphere Y 1. Negative Negative 2. Positive Positive 3. Zero Zero 4. Positive Negative correct 5. Negative Positive Explanation: The force is repulsive if the charges are of the same sign, so when the negatively charged rod moves close to the sphere X , the neg- atively charged electrons will be pushed to sphere Y . If X and Y are separated before the rod moves away, those charges will re- main on X and Y . Therefore, X is positively charged and Y is negatively charged. 003 10.0 points Two initially uncharged conductors X and Y are mounted on insulating stands and are in contact, as shown below. A negatively charged rod is brought near but does not touch them. With the rod held in place, con- ductor Y is moved to the right by pushing its stand, so that the conductors are separated. X Y − − − − Which of the following is now true of con- ductor Y ? 1. It is negatively charged. correct 2. It is at the same potential that it was before the charged rod was brought near. 3. It is positively charged. 4. It is uncharged. 5. It is charged, but its sign cannot be pre- dicted. Explanation: Because the negatively charged rod is held sicher (gns249) – H1ElFieldsDiscrete – Avram – (1956) 2 near conductor X , the electrons in the con- ductor are pushed away from the rod, which makes conductor Y negatively charged. Once the two conductors are separated, conductor Y will remain negatively charged even when the rod is removed. 004 10.0 points 1) Two uncharged metal balls, X and Y , stand on glass rods and are touching. Y X 2) A third ball, carrying a negative charge, is brought near the first two....
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This note was uploaded on 06/15/2010 for the course PHYS 1401 taught by Professor Av during the Summer '10 term at Austin Community College.
- Summer '10