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Homework Help: Question about potential difference?

  1. Mar 31, 2013 #1
    Question about potential difference??

    1. The problem statement, all variables and given/known data

    A very long wire carries a uniform linear charge density λ
    Using a voltmeter to measure potential difference, you find that
    when one probe of the meter is placed 2.5 cm from the wire and
    the other probe is 1cm farther from the wire, the meter reads 575 V
    (a) What is λ?

    2. Relevant equations

    Va-Vb= λ/2∏ε0 * ln(rb/ra)

    3. The attempt at a solution

    My first question is what does the voltmeter read? Va-Vb or Vb-Va? ... In this case I assume it is Vb-Va.. So in our attempt it should be -575= λ/2∏ε0 * ln(3.5/2.5) .. But this doesn't yield to the answer... Any thoughts!?
  2. jcsd
  3. Mar 31, 2013 #2
    The question only says that |Vb-Va| is 575 V. So you can only find|λ|.
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