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Unformatted text preview: PHY 2049, Spring 2009 Test 1 Name and PID: Please PRINT your name To get full credit you MUST show your work. Use the space provided including the reverse side of each sheet. Write your names on any additional sheets used. Possibly useful information (formula sheet) is provided. Section A (each 2 points) are short descriptive questions. Please read statements for each question and circle the correct statement (answer). Section B requires calculations/derivations. Please be as clear as possible explaining the notations, symbols etc. Section A 1. Three concentric conducting shells have radii R 1 < R 2 < R 3 and charges -3Q, +Q and +4Q, respectively, where Q is some positive number. What is the charge on the inner surface of the innermost shell? (a) +2Q (b) -2Q (c) +4Q (d) -Q (e) 0 Answer: (e) The electric field must be zero inside the innermost conductor 2. Two point charges, q 1 = 2 q and q 2 = + q , are fixed at positions on the x-axis, as shown below. If you were to place a third point charge somewhere so that the force on it would be zero, you should place that charge somewhere a) on the x-axis to the right of the two charges, b) on the x-axis in between the two charges, c) on the x-axis to the left of the two charges, or d) off of the x-axis. Answer: (a) 3. You bring a positively charged rod toward a hanging sphere on a thread. At first, as you bring the rod towards the sphere, the sphere is repelled. Eventually, however, when the rod is very close to the sphere, the sphere is attracted to the rod. Assuming that no...
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