# Quiz7Electricity1Answer - stands that are 1.75 m apart The...

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AP1200 Quiz 7 Student Name ____________________________ Student ID ___________________ 1. A balloon is negatively charged by rubbing and then clings to the wall. Does this mean that the wall is positively charged? Why does the balloon eventually fall? Answer No. The balloon induces charge of opposite sign in the wall, causing it to be attracted. The balloon eventually falls since its charge slowly diminishes as it leaks to the ground. Some of the charge could also be lost due to ions of opposite sign in the surrounding atmosphere which could tend to neutralize the charge . 2. Two identical metal spheres with excess charges of –q and +3q are placed on insulated
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Unformatted text preview: stands that are 1.75 m apart. The magnitude of the force between the two spheres is F. The spheres are touched together and then returned to their original insulated stands. What is the magnitude of the force between the spheres now? Answer: F’ = (1/3)F After the two spheres are touched together: the net charges +2q are shared by the two spheres; so each sphere gets +q. We have F’ = kq 2 /r 2 Before the two spheres are touched together: F = -3kq 2 /r 2 So the magnitude of F’ is 3 times smaller than F....
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## This note was uploaded on 01/11/2011 for the course AP 1200 taught by Professor Michela.vanhove during the Spring '10 term at City University of Hong Kong.

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