# HW3soln - Physics 21 Fall 2007 Visualizing Electric Field...

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Physics 21 Fall 2007 Solution to HW-3 Visualizing Electric Field Lines (A) For a sheet of negative charge, the field is (B) This diagram is wrong because field lines cannot cross each other, and because symmetry requires the field lines to be parallel. (C) The field of an electric dipole is (D) This diagram is wrong because the field lines should be smooth curves, and the field lines should always end on negative charges at infinity. (E) From the diagram we can see Q _A > 0 and Q _B < 0 from the direction of the field lines. The lines are more dense near Q _A, so | Q _A| > | Q _B|. Only the second choice (Q_A = +7 q , Q _B = -3 q ) satisfies both these relations. Electric Field inside a Conductor (B) The electrons move to the left, and the nuclei are almost stationary (the nuclei move slightly to the right). The nuclei are much more massive than the electrons, so their acceleration a = F/m = eE/m is much less. (C) The left end is negative and the right end positive, because of
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## This note was uploaded on 02/29/2008 for the course PHYSICS 21 taught by Professor Hickman during the Spring '08 term at Lehigh University .

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