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Charge, Potential, Work, and Electricity

  1. Mar 12, 2009 #1
    SOLVED



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

    Moving a charge from point A, where the potential is 275 V, to point B, where the potential is 150 V, takes 4.0 10-4 J of work. What is the value of the charge?


    2. Relevant equations

    V= w/q

    V= change in voltage
    w= work
    q= charge

    3. The attempt at a solution

    This problem seems simple enough, but for some reason I can't get the right answer. W= 4E-4 and then I divided it by the change in V (275- 150).

    4E-4/ 115= 3.478E-6

    Then I mulitplied by 1E6 to change the units into micro-Coulombs.

    Yet this answer is wrong. What am I doing incorrectly??

    Thanks in advance for the help!

    ~Phoenix
     
    Last edited: Mar 12, 2009
  2. jcsd
  3. Mar 12, 2009 #2

    lanedance

    User Avatar
    Homework Helper

    first 150-275 = 125 not 115

    i thin you may have to be careful with signs here as well

    hint dV = V2-V1, if it takes work to move a charge to a smaller potential can we say something about the charge?

    Think which way the electric field is pointing and how a positive charge would want to move between the points
     
  4. Mar 12, 2009 #3
    Oh.... I see what you're saying. (Sorry about the 115 thing, that was just my typing... the actual calculation was correct).

    So instead it would be 4E-4/(150-275)= -3.2 Micro-C. Thanks so much! That makes perfect sense.
     
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