
#1
Sep1109, 04:06 PM

P: 34

A nonconducting, spherical shell centered at the origin has radius r1 and total charge Q, where Q is a positive value. (DO NOT ASSUME THE POTENTIAL AT INFINTIY IS ZERO!)
http://i662.photobucket.com/albums/u...Cpotential.gif 1) The electric potential just outside the surface of the shell is __________ the electric potential infinitely far from the shell. A) higher than B) lower than C) equal to  This problem stumped me. I figured that the electric potential outside the sphere was... V = Q/(4*pi*EpsilonNot*r) So as r grows, the potential actually gets higher. So the answer is B.  2) If a negative charge outside the shell is moved closer to the shell, the potential energy of the system will __________. If a positive charge outside the shell is moved closer to the shell, the potential energy of the system will __________. A) decrease, increase B) increase, stay the same C) increase, decrease  Since the force and displacement vectors are acting in opposite directions, the total work decreases. PE = W, so then that means that the potential energy increases. The opposite is true with the positive charge. So the answer is C.  Can somebody please confirm these answers? I would like to know if I messed up some logic along the way. Thanks in advance! 


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