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227f11hw03ans

# 227f11hw03ans - MasteringPhysics Assignment Print View...

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H3 Electric Potential, Dipoles (23.1-5, 21.7) Due: 11:59pm on Monday, September 26, 2011 Note: You will receive no credit for late submissions. To learn more, read your instructor's Grading Policy Exercise 23.2 Description: A point charge q_1 is held stationary at the origin. A second charge q_2 is placed at point a, and the electric potential energy of the pair of charges is + 5.4 * 10^( - 8) J. When the second charge is moved to point b, the electric force on the... A point charge is held stationary at the origin. A second charge is placed at point , and the electric potential energy of the pair of charges is . When the second charge is moved to point , the electric force on the charge does of work. Part A What is the electric potential energy of the pair of charges when the second charge is at point ? Express your answer using two significant figures. ANSWER: Electric Potential Energy of Three Point Charges Description: Calculate the electric potential energy of three identical charges at the corners of an equilateral triangle. Part A Three equal point charges, each with charge 1.75 , are placed at the vertices of an equilateral triangle whose sides are of length 0.550 . What is the electric potential energy of the system? (Take as zero the potential energy of the three charges when they are infinitely far apart.) Hint A.1 How to approach the problem Use the equation for the electric potential energy between two point charges to calculate the energy for each interaction between two of the three point charges. The sum of these energies will be the total electric potential energy. Be careful to avoid double counting. Settings per Student Student View Summary View Diagnostics View Print View with Answers MasteringPhysics: Assignment Print View http://session.masteringphysics.com/myct/assignmentPrintView... 1 of 17 9/12/11 2:50 PM

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Hint A.2 Find the electric potential energy of one pair Assume that one charge is interacting with a second charge, ignoring any effects from the third charge. What is the electric potential energy for this single interaction? Hint A.2.1 Electric potential energy of a pair of charges Recall that the electric potential energy between two charges and separated by a distance is given by the formula . Express your answer in joules to three significant figures. ANSWER: = Since the charges are at the vertices of an equilateral triangle, each pair of charges will be 0.550 apart, no matter which two charges are selected. This fact, coupled with the fact that the charges are identical, means that all pair interactions are identical. Hint A.3 How many interactions are there? How many pair interactions are there for the three charges? Hint A.3.1 Double counting It is important to keep in mind that a pair of charges can interact only once, so if the first charge is interacting with the second charge for one pair, the interaction of the second charge with the first charge cannot also be used, since the pair has already been counted.
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