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Homework Help: Electric fields and equipotentials

  1. Jan 26, 2009 #1
    1. The problem statement, all variables and given/known data

    The figure below shows a test charge q between the two positive charges. Find the force (in newtons) on the test charge for q = -4 µC.
    a)Give a positive answer if the force is to the right and a negative answer if the force is to the left.
    wpl2.jpg

    b.)For the previous question, find the electric field (in newtons/coulomb) at the position of test charge. Again, supply a positive value if the electric field points to the right and a negative value if it points to the left.

    2. Relevant equations
    F=ke|q1|q2|/r^2
    E=F/qo


    3. The attempt at a solution
    a)F21=ke(2x10-6)(4x10-6)/(3x10-2)^2 = 80 to the left
    F23=ke(4x10-6)(3x10-6)/(2x10-2)^2 = 269.7 to the right
    F2 = 190

    b)E=190/-4x10-6 = -4.75e7



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

    How much work (in joules) is done in moving a charge of 2.5μC a distance of 22 cm along an equipotential at 9~V?

    2. Relevant equations
    W=-change in PE, where PE = q(change in volts)


    3. The attempt at a solution

    W=-2.5e-6(9)= -2.25e-5 J
     
  2. jcsd
  3. Jan 26, 2009 #2
    Hmm I'm not sure about the negative for qo
     
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