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Unformatted text preview: 5/10/09 3:39 PM MasteringPhysics Page 1 of 12 http://session.masteringphysics.com/myct Assignment Display Mode: View Printable Answers phy260S09 HW11 Due at 11:00pm on Tuesday, May 5, 2009 View Grading Details Energy Stored in a Charge Configuration Description: Find the work required to assemble four charges of the same magnitudethree positive, one negativeat the corners of a square. Four point charges, A, B, C, and D, are placed at the corners of a square with side length . Charges A, B, and C have charge , and D has charge . Throughout this problem, use in place of . Part A If you calculate , the amount of work it took to assemble this charge configuration if the point charges were initially infinitely far apart, you will find that the contribution for each charge is proportional to . In the space provided, enter the numeric value that multiplies the above factor, in . Hint A.1 How to approach the problem The Coulomb force is conservative. If we define the potential energy of the system to be zero when the charges are infinitely far apart, the amount of work needed to place any one charge in a configuration is equal to its electric potential energy. Imagine moving charge A, then B, then C, and finally D into place. Find the work required to add each charge to the configuration by calculating the potential energy of each just after it is added. Add the work required for each charge to find the total work required. Hint A.2 Electric potential and potential energy Recall that the electric potential at a point at distance from a charge is , where . Note that this equation implicitly defines the electric potential to be zero at . The electric potential energy of a charge is equal to , where is the electric potential at the position of the charge before the charge is placed there. To find the potential at a point due to multiple charges, sum the potentials at that point due to each charge. Hint A.3 Work required to place charge A What is , the work required to assemble the charge distribution shown in the figure? Hint A.3.1 Find the potential at the location of charge A What is , the electric potential at the upper left corner of the square before charge A is placed there? [ Print ] 5/10/09 3:39 PM MasteringPhysics Page 2 of 12 http://session.masteringphysics.com/myct Express your answer in terms of some or all of the variables , , and . ANSWER: = 0 Express your answer in terms of some or all of the variables , , and . ANSWER: = 0 Hint A.4 Work required to place charge B What is , the amount of work required to add charge B to the configuration, as shown in the figure? Hint A.4.1 Find the potential at the location of charge B What is , the potential at the upper right corner due to charge A, before charge B is placed there?...
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 Charge, Potential Energy, Electric charge, Fundamental physics concepts

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