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Unformatted text preview: Physics 21 Fall, 2008 Solution to HW-6 Electric Fields and Equipotential Surfaces The dashed lines in the diagram represent cross sections of equipotential surfaces drawn in 1 volt increments. (a) What is the work W AB done by the electric force to move a 1 C charge from A to B ? (b) What is the work W AD done by the electric force to move a 1 C charge from A to D ? (c) Compare the magnitudes of the electric fields at C and B . (a) zero; A and B are on same equipotential surface. (b) 1 volt 1 C = 1 Joule (c) E (the field magnitude) at C is greater than E at B , because the equipotential lines are closer together at C . 23-47 In a certain region, the electric potential is V ( x, y, z ) = Axy Bx 2 + Cy , where A , B , and C are positive constants. Find E x , E y , and E z . Where is the electric field zero (multiple choice)? E x = V x = Ay + 2 Bx E y = V y = Ax C E z = V z = 0 From the second equation, E y = 0 when x = C/A . Then (from the first equation) E x = 0 when Ay + 2 B ( C/A ) = 0 y = 2 BC/A 2 ....
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