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Homework Help: REALLY easy electrostatic question

  1. Dec 9, 2013 #1
    So I'm getting confused by my textbook, and having problems finding any straight forward answers online. I am studying Gr.12 physics myself, so I don't have a teacher. I understand the nature of charges, but somehow I'm getting mixed up when dealing with non-conductive materials. Basically, I don't see how they can actually transfer a charge through conduction. My understanding is that at best they can transfer a charge from the point of contact. To make things worse, I'm doing a review section on electrostatics, and I find something contradictory. Let me explain:

    "In each of the following examples, identify the charge on each object and state the method of charging the object"

    b) "A glass rod is rubbed with silk and then is touched to a neutral metal sphere"

    The answer states: "The glass rod will be positive, the silk will be negative, and the sphere will be
    positive. In the rubbing process, the rod and the silk become charged by friction.
    When the rod touches the sphere, the sphere becomes similarly positively charged
    by conduction"

    So I understand that that the glass rod could charge the sphere through induction, but conduction? Either way, I would accept that the glass rod could charge the sphere through conduction, if it wasn't for this other question, which seems to contradict it.

    It's a diploma exam question, and it basically shows two electroscopes with their leaves spread. It then says:

    "A student touches electroscope I with a neutral metal rod" and then "The student touches electroscope II with a neutral glass rod"

    "Which of the following diagrams best shows the leaves of the electroscopes after the electroscopes are touched with the rods"?

    The answer is that the electroscope touched by the metal rod has closed leaves (transferred it's charge) and the other electroscope (glass rod) is unchanged ( I assume didn't transfer it's charge )

    So I'm trying to understand this, and just when I think I do, I don't!. Can someone perhaps shed some insight and allow me to understand what is really happening?!
  2. jcsd
  3. Dec 9, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Nah. Charge will not flow from (or to) the insulating rod.

    I agree with that.

    You might want to read the following to solidify your thinking: Charging by Conduction
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