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Electrostatics Questions

  1. Apr 11, 2005 #1
    Hello everyone! I've recently been messing around and experimenting with electrostatics and have some questions I cant find answers to. Ok here they are:

    1. If I understand this correctly a neutral object is attracted to positive and negatively charged objects. If this is true, why does this happen? Shouldnt the neutral object not respond to electric fields since its net charge is 0?

    2. According to the triboelectric series air always gives electrons to just about everything else when they come into close contact. Then since air is touching everything is it possible to give something a static positive charge?

    3. If you have an object that is charged at -1 and another at -7 will they seek each other out so each object has a charge of -4 and then repel each other only after they have equalized, or will they repel each other to begin with?

    4. If you rub styrofoam with fur the styrofoam picks up a negative charge and affects a stream of water, but its force slowly weakens and strands of rabbit fur that were stuck to the styrofoam will be 1) attracted to the water stream and 2)start flying off the styrofoam after its affect on the water has significantly weakened. Why?

    Ok I've taken a stab at answering my fourth question but I still cant figure it all out. Im assuming water molecules have a net positive charge and thats why the stream of water is attracted to the styrofoam. But I cant figure out why the styrofoams force on the water slowly weakens over time and after a while the strands of rabbit fur start flying off the styrofoam?

    Thank you for your help everyone!
     
  2. jcsd
  3. Apr 11, 2005 #2

    dextercioby

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    For the first it's more complicated.The so-called "multipolar fields/potentials" may come into play,meaning that the neutrality would not be worth too much.

    As for #3,the electrons would seek to equate the potentials.It's typical for a transport phenomenon.

    Daniel.
     
  4. Apr 11, 2005 #3

    Meir Achuz

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    Some answers:

    1. The neutral object gets "polarized". That is the molecular electrons get displaced slightly by the E field of the charged object, so that the neutral object
    develops an electric dipole moment. The E field from the charged object then exerts a force on the electric dipole moment.

    3. Any magnitude of two negative charges will repel each other. They don't have to be equal.

    2. and 4. require a bit more of a descriptive (time consuming) answer.
     
  5. Apr 11, 2005 #4

    Meir Achuz

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    2. Yes, this happens when airplanes fly through air at high speed. The wings acquire a charge. As this charge leaks off the wing, it ionizes the nearby air.
    The ions then attract water molecules, forming droplets which we see as "jet trails".
     
  6. Apr 11, 2005 #5

    Meir Achuz

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    4. Several steps take place, each which you have carefully observed.
    I. The styrofoam gets positively charged and attracts the neutral water drops as in answer 1.
    II. The fur is negatively charged, and so sticks to the styrofoam.
    III. The charge on the styrofoam slowly leaks off into the surrounding air.
    IV. The negative charge on the fur becomes stronger than remaining positive charge on the styrofoam. Thus, is the attractive force between the water and the fur
    is strong enough for the strands of fur to reach out toward the water.
    V. When the charge on the styrofoam gets small enough, the force of the water on the fur pulls it off the styrofoam
     
  7. Apr 11, 2005 #6
    Yep. It's called "electrostatic induction."
     
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