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Homework Help: Question about electric force.

  1. Feb 2, 2006 #1
    This is a four part question

    Q1> A small cork with an excess charge of +5.o C is placed 0.10m from another cork, which carries a charge of -3.1C. The Coulomb constant is given. What is the magnitude of electric force between the corks.

    A1> I will be using F = kq1q2/R-squared. The only thing that is throwing me off is... why would the question say excess charge and not just charge. any comments?

    Q2> is this force attractive or repulsive
    A2> attractive ofcourse

    Q3>Now this is the part that I am having trouble with.
    How many excess electrons are on the negative cork?
    A3> Is there some fundamental idea that I am missing here? I dont know how to do this part.

    Q4>How many electrons has the positive cork lost?
    A4> dont know this one either. Maybe this will become more evident after I know how to solve Q3.

    Can anyone help please.

    Thanks in advance
  2. jcsd
  3. Feb 2, 2006 #2
    do you know the fundamental charge of the electron?
  4. Feb 2, 2006 #3


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    Gold Member

    When an object has positive charge that means that there are more positive charges than negative ones. If it's negativly charged then it has more negative charged particles (electrons) than positive ones. If the amount is equal then it has a neutral charge.
  5. Feb 2, 2006 #4
    ohhh ok.

    In my book I have 1e = this much C (charge) ... i dont remember the number exactly but I can look it up in my book.

    So for question 3 all i need to do is take the charge of q1 which is given to be +5C and divide it by the charge in 1e and that will give me the answer. Thanks andrewchang. Can you confirm my reasoning above.

    So what am I missing in question 4. How would I approch Q4.

    PS Daniel thanks for that explanation on positive and negative charge.
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