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How to determine the positive or negative charge?

  1. Mar 7, 2012 #1
    images?q=tbn:ANd9GcRRsLB6wUKEON5YRL9RD0iBTWqFzkFGrjExNCSyzpFWwjADAfQ_.jpg

    Red is for + and Black is for -.

    images?q=tbn:ANd9GcQxMF9h8qAI1V_yUx2ycue_98QiS_2aqx74bfp-VzJua5AUjpZ4kw.jpg

    If I place red rod into positive side of battery and place black rod into negative side of battery, it displays +9V.

    If my hand is touching the black rod, and the red rod is touching the ground, then it displays a negative value,
    I would like to know whether my body is carrying positive or negative charges as it compares to the ground.
    Does anyone have any suggestions?
    Thanks in advance for any suggestions
     
  2. jcsd
  3. Mar 7, 2012 #2

    cmb

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    This is generally a function of the meter, rather than a measurement of your 'potential'. All you achieve in this scenario is present the meter with what it sees as a floating potential, because your resistance will be higher than the meter's own resistance. However, you will likely see some few 10's or 100's mV flash up due to the way the meter interprets that, plus, maybe, your sweaty body and fingers may create certain conductive paths (and possibly electrochemical reactions between your salty sweat and the nickel plated probes).
     
  4. Mar 7, 2012 #3
    So in this case, is my body carrying more positive or negative charges as it compares to the ground?
    Does anyone have any suggestions?
    Thanks in advance for any suggestions
     
    Last edited: Mar 7, 2012
  5. Mar 7, 2012 #4

    vk6kro

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    The charge on your body is usually low but if you walk across a carpet with plastic shoes on, you can build up a large charge due the relative properties of the carpet and your shoes.

    You may not be aware of this until you touch something metallic that is grounded, when you can get a very obvious shock.

    For some reason this seems to happen at airports a lot.

    There is a table of the relative properties of various insulators here:
    http://en.wikipedia.org/wiki/Triboelectric
    See the chart at the right,
    For example, if you rub rabbits fur on ebonite the ebonite gets a negative charge and the fur gets a positive charge.

    Your body is basically a big bag of conductive liquid, so it tends to take on whatever potential your shoes develop.

    People working with some types of electronic components have to wear a conductive wrist band to avoid them building up a charge and possibly zapping the electronics.
     
  6. Mar 8, 2012 #5
    If my hand is touching the black rod, and the red rod is touching the ground, then it displays a negative value. Does anyone have any suggestions on whether my body is carrying positive or negative charges as it compares to the ground?
    Thanks in advance for any suggestions
     
  7. Mar 8, 2012 #6

    vk6kro

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    Positive.

    If it was a charge, though, it would decrease in value as you watch it.

    Did this happen? What reading do you get?

    It is far more likely that the meter is picking up mains interference or a local broadcast station as has already been mentioned.
     
  8. Mar 8, 2012 #7
    The reading is decreasing in value, Let ignore any interference in this case, do you have any suggestions on what charges (positive or negative) is hold within my body as comparing with the ground? +ve or -ve on my body.
    Thanks everyone very much for any suggestions
     
  9. Mar 8, 2012 #8

    vk6kro

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    You are not listening.

    The charge would be positive.

    If you reversed the leads on your multimeter, then the negative sign would go away, indicating that the polarity was correct when the positive lead was going to your body.
     
  10. Mar 8, 2012 #9

    cmb

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    I think you are asking if a human body typically becomes positively or negatively charged.

    It doesn't do either, but may become charged either way because of a variety of factors, most likely your clothes rubbing on your body, but possibly your shoes rubbing on the floor, particles in the air, what you've just been touching, whatever. No particular preference one way or the other, but I dare say that some particular piece of clothing will result in one polarity of charge, whereas another does the opposite.
     
  11. Mar 8, 2012 #10

    vk6kro

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    I notice in the Tribo-electric series chart:

    http://en.wikipedia.org/wiki/Triboelectric

    that air is just above human skin and a little more above human hair. So you might get a slight negative charge if you were running in dry air.

    Almost any kind of clothing would develop a stronger negative charge in dry air if there was some relative movement.
     
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