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Work and change in voltage

  1. Feb 19, 2012 #1
    1. The problem statement, all variables and given/known data

    Known:

    Potential Difference of range 0.16 m < r < infinity is -562 kilovolts
    At r = 0.16 there is a -10 μC charge on a conducting sphere


    Question:

    How much work would the field do if a proton were moved from infinity to 0.16m? comment on the meaning of the sign.

    2. Relevant equations
    W = -ΔU = -q * ΔV
    1 e = 1.60 x 10 ^-19 C
    1 proton = +1e

    3. The attempt at a solution

    q = 1.60 x 10 ^-19 C
    ΔV = -562 kV
    W = -q * ΔV
    ... = -1.60 x 10 ^-19 C * -562 kV
    ... = 89.9 x 10 ^-15 J

    However, shouldn't a proton wan't to approach a negative charge and thus the work should be negative?
     
  2. jcsd
  3. Feb 19, 2012 #2

    vela

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    The proton is brought in from infinitely far away to r=0.16 m. It moves toward the negative charge, and the force on it due to the field also points toward the negative charge, so the work should be positive, no?
     
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