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Charging and Discharging

  1. Sep 3, 2008 #1
    1. The problem statement, all variables and given/known data
    You observe that a negatively charged plastic pen repels a charged piece of magic tape. You then observe that the same piece of tape is repelled when brought near a metal sphere. You are wearing rubber soled shoes, and you touch the metal sphere with your hand. After you touch the metal sphere, you observe that the tape is attracted to the metal sphere. Which of the following statements could be true? Check all that apply.

    Possible answers:

    1. Electrons from the sphere moved into the salt water on your skin, where they reacted with sodium ions.

    2. The excess negative charge from the sphere spread out all over your body.

    3. Chloride ions from the salt water on your hand moved onto the sphere.

    4. Sodium ions from the salt water on your hand moved onto the sphere.

    5. Electrons from your hand moved onto the sphere.

    6. Electrons from the sphere traveled through your body into the Earth.

    7. After you touched it, the metal sphere was very nearly neutral.

    3. The attempt at a solution
    I have 3 total attempts at this (it is an online homework system, and although the problem seems very easy and basic, I have missed it twice.) My first try I selected answers: 1,2,4,6, and 7. On my second attempt I selected: 2,6, and 7. I really though my first attempt was correct, and now I am lost. Any help would be appreciated, thanks.

    I know (or at least I think I know), that there is no way that electrons/Cl- ions could transfer from your hand to the ball because of its negative charge. All the other answers seem logical, in that the charge is being dissipated into your body/skin, and that the metal sphere then becomes uncharged, I think I may be missing something though?
     
    Last edited: Sep 3, 2008
  2. jcsd
  3. Sep 3, 2008 #2
    I have only about 3 and a half hours until my assignment is due, so any help would be appreciated. I really do not know where my logic is wrong, the more and more I look at it, the more confused I become.
     
  4. Sep 4, 2008 #3
    anyone have any ideas on this problem? I tried 1, 2, 6, and 7, but that also did not work.
     
  5. Sep 3, 2010 #4
    This may be a few years too late but you are wearing tubber soled shoes so that would rule out #6 as rubber is acting as an insolator between you and the earth. Your first attempt was correct minus the 6.
     
  6. May 24, 2011 #5
    i KNOW IT'S TOO late! but i will say the probable answers are 1 and 4 only. and about the 7th one i will say the sphere is nearly neutral not purely,and also the amount of charge on the magic tape is not so large that it will result into big electric polarisation of sphere and result in net attraction b/w them (even though little -ve charge is present on sphere.)
    In the given options above i will vote 1 and 4 only and rest seems to me perfectly incorrect!
     
  7. Sep 10, 2012 #6
    Even more late!

    I just completed this hw assignment (and for GT as well, no less!), and here are, officially, the correct answers:

    Electrons from the sphere moved into the salt water on your skin, where they reacted with sodium ions.

    After you touched it, the metal sphere was very nearly neutral.

    Sodium ions from the salt water on your hand moved onto the sphere.

    The excess negative charge from the sphere spread out all over your body.
     
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