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Unformatted text preview: Manage this Assignment: 1. Electric Forces and Fields Due: 11:00pm on Thursday, January 14, 2010 Note: To understand how points are awarded, read your instructor's Grading Policy . Print Version with Answers Charging a Conducting Rod Description: This problem explores the behavior of charge on conductors This problem explores the behavior of charge on conductors. We take as an example a long conducting rod suspended by insulating strings. Assume that the rod is initially electrically neutral. For convenience we will refer to the left end of the rod as end A, and the right end of the rod as end B. In the answer options for this problem, "strongly attracted/repelled" means "attracted/repelled with a force of magnitude similar to that which would exist between two charged balls. Part A A small metal ball is given a negative charge, then brought near (i.e., within about 1/10 the length of the rod) to end A of the rod . What happens to end A of the rod when the ball approaches it closely this first time? Hint A.1 The key property of conductors The key property of a conductor is that the charges are free to move around inside in response to internal electric fields; in a static situation, they will arrange so that the internal field is zero. Hint A.2 How much charge moves to end A? It is stated that the ball is much closer to the end of the rod than the length of the rod. Therefore, if points down the rod several times the distance of approach (but still much closer to end A than end B) are to experience no electric field, the charge on end A of the rod must be comparable in magnitude to the charge on the ball (so that their fields will cancel). ANSWER: It is strongly repelled. It is strongly attracted. It is weakly attracted. It is weakly repelled. Page 1 of 32 MasteringPhysics: Assignment Print View 1/8/2010 http://session.masteringphysics.com/myct/assignmentPrint?assignmentID=1323344 Now consider what happens when the small metal ball is repeatedly given a negative charge and then brought into contact with end A of the rod. This charge is said to be "induced" by the presence of the electric field of the charged ball: It is not transferred by the ball. It is neither attracted nor repelled. Part B After a great many contacts with the charged ball, how is the charge on the rod arranged (when the charged ball is far away)? ANSWER: There is positive charge on end B and negative charge on end A. There is negative charge spread evenly on both ends. There is negative charge on end A with end B remaining neutral....
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