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Homework Help: Question concerning Electromagnetism

  1. Jan 27, 2013 #1
    Here is a homework question that I have for my general physics class; our professor ran out of time during lecture and did not get to explain the material very well so I am a little lost.

    A 47.0 g ball of copper has a net charge of 1.7 µC. What fraction of the copper's electrons have been removed? (Each copper atom has 29 protons, and copper has an atomic mass of 63.5.)

    I know that it is going to involve some stoichiometry-type solving, but I just can't seem to figure it out
  2. jcsd
  3. Jan 28, 2013 #2
    How many electrons does the ball have when not charged?
  4. Jan 28, 2013 #3


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    Homework Helper
    Gold Member

    Yes, you will have to check out what a coulomb is in terms of 'elementary charges' (which is best to look on Wiki because of the relations to other things you'll find there, and look also for ampere) and revise what mole and atomic mass mean.

    In my day mnyah mynah the calculation would have been a bit more direct because then the coulomb was defined in terms of electrochemical measurements, the amount of silver deposited by the flow of current in silver nitrate, something very acceptably precisely measurable, so the given number of coulombs [itex]\equiv[/itex] a number of moles of Ag [itex]\equiv[/itex] half that number of moles of Cu considering the atomic charges.

    That old definition has been superseded because even more precisely measurable standards have been evolved but it would still be good enough for the calculation asked here.
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