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Unformatted text preview: 1 PHYS 1304 Midterm Exam Name ID 1. (Total 30 points) Two point charges, q 1 and q 2 , are fixed in space. The distance between the two charges is d . Here q 1 = 2.0 C, q 2 = 8.0 C, and d = 9.0 cm. 1 C = 106 C. (a, 20 points) Find the point in space that is close to the two charges where the electric field is 0. (b, 10 points) Now you move a charge q 3 from infinitely far away to this point, how much work you have to do during this process when q 3 = 1.0 C? The Coulomb constant k e = 8.99 10 9 N m 2 /C 2 . (c, bonus 5 points, do it when you have time in the end) Is q 3 in a stable or unstable equilibrium condition? Would your answer change if q 3 = 1.0 C? q 1 q 2 p o x 9.0 cm x 2 e q E k r = One dimensional problem. Construct the coordinate as shown. For (a) the formula to use is The equation: ( ) 1 2 2 2 9 0 e e q q k k x . x = ( ) 2 2 2 0 8 0 9 0 . . x . x = or: Solve for x , we have 3 0 cm or 9 0 cm (discard) x . x . = =  So x = 3.0 cm is the point where the electric field is 0....
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This note was uploaded on 05/06/2008 for the course PHYS 1304 taught by Professor Ye during the Spring '08 term at SMU.
 Spring '08
 Ye
 Charge, Magnetism

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