Sep11-09, 05:06 PM
A non-conducting, 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!)
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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