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Unformatted text preview: song (shs546) Practice HW 1 Solutions weathers (22202) 1 This print-out should have 6 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 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 Positive 2. Negative Negative 3. Positive Negative correct 4. Positive Positive 5. Zero Zero 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. 002 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. Y X- 3) Then the first two balls are separated from each other, Y X- 4) and the third ball is finally removed. Y X When this is all four steps are done, it is found out that 1. Balls X and Y are both positive. 2. Balls X and Y are both negative. 3. Ball X is positive and ball Y is negative. 4. Balls X and Y are still uncharged. 5. Ball X is negative and ball Y is positive. correct Explanation: When a negative ball is moved near a metal- lic object ( X and Y ), the negative charge will attract positive charges, causing X to have excess negative charge and Y to have excess positive charge ( X and Y are in contact, so the total net charge on X and Y should be zero). song (shs546) Practice HW 1 Solutions weathers (22202) 2 +-- Later, X and Y are separated, retaining their charges, so when the third ball is finally removed, X will have net negative charge and Y will have net positive charge....
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- Spring '00