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Physics/Just a general question (nothing related to class or homework) related to conservation of charge concept.


I noticed that when many textbooks or websites explain the concept of conservation of charge, they always use the example of neutrality, whereby when one object gains an electron, it loses an equal amount proton. If textbooks discuss problems regarding CHARGED spheres of different magnitudes (for example, +5 microboloumbs and -3 microcoloumbs) why do they not use them as examples? Does conservation of charge really state that you can just add the two up to find the total charge? Yes, the law states charge is CONSTANT, however, it bothers me that it's always NEUTRAL objects being explained at the heart of it. Does constant mean for any process regardless if the two objects are neutral or charged already when adding them up? Thanks in advance.

In order to make a neutral object positive you remove electrons. To make a neutral object negative you add electrons. Generally speaking only the electrons are free to move around. The protons, by comparison are trapped within the nucleii of the substance and are not free to move around.
If you have a conducting sphere with a charge of -5 uC that means that the sphere has an EXCESS of electrons. An otherwise identical sphere with a charge of +5 uC has a shortage of the same number of electrons. If you touch the two sphere together the excess electrons on the negative sphere will move to the positive sphere and will make both spheres neutral.


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James J. Kovalcin


I am teaching or have taught AP physics B and C [calculus based mechanics & electricity and magnetism] as well as Lab Physics for college bound students. I have a BS in Physics from the University of Pittsburgh and a Master of Arts in Teaching from same. I have been teaching physics for 34 years. I am constantly updating my skills and have a particular interest in modern physics topics.

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