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Homework Help: Triboelectrics Help please.

  1. Aug 29, 2005 #1
    Triboelectrics.... Help please.

    this problem is a worked example in my textbook.. but it looks like they have just pulled numbers from thin air. I really dont understand how they got these answers.. can anyone explain?

    A perspex rod is rubbed with a piece of silk. it acquires a charge of 0.02uC

    a) How many electrons are transferred?
    b) is this charge is now transderred to an electroscope with charge +0.01uC what will be the net state of the electroscope?

    Book's Solution:
    0.02 x 10^-6 x 6.25 x 10^18 electrons -or-
    a) 1.25x10^-11 electrons transferred.

    b) total charge on the electroscope after transfer:
    0.02uC + 0.01uC = 0.03uC (+)
    the electroscope leaf deflection will increase and the net charge on the electroscope is now +0.03uC = 1.87x10^11 electrons depleted

    I really dont understand, can anyone help?
    Last edited: Aug 29, 2005
  2. jcsd
  3. Aug 29, 2005 #2
    okay here you go.

    1 uC ( micro-columb ) = 1 * 10^-6 C

    Charge on 1 electron = 1.6 x 10^-19 C

    Number of electrons in 1 Columb = 1/(1.6 * 10^-19)
    Which = 6.25 * 10^18 -points solution-

    Amount of charge transfered = 0.02 * 10^-6 (points micro columb value above)
    Amount of electrons transfered = Amount of charge transfered * number of electrons/C


    0.02 * 10^-6 * 6.25 * 10^18 = 1.25 * 10^-11 (electrons transfered)

    For b, when u rub the rod with a piece of silk, it aquires a negative charge yeah?(electrons go from the rod to the silk)

    So, if u transfer this charge to the electroscope, which already has +0.01uC, its total charge becomes +0.03uC
    +0.02uC +0.01uC = +0.03uC

    The deflection increases cuz like-charges repel, so if i have a higher charge on the scope, the leaves both possess a higher charge, and thus experience more repulsion.

    1.87 * 10^11 ?
    i think u meant 1.87 * 10^-11
    that'll be the number of electrons the electroscope is missing, if u calculate, that equals to 0.03uC

    Thank ruby for this.. her fault
  4. Aug 29, 2005 #3
    thank catherine for this, her fault