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Homework Help: Couple More Questions on Electrostatics

  1. Jan 3, 2007 #1
    1. The problem statement, all variables and given/known data
    1) From the observation that there's an electrostatic attraction between object A and B, what's the most you can conclude about the electric charge on A and B?

    2) A plastic sphere with a positive charge of 4.8E-19 C is held stationary in a gravitational field of strength 9.8m/s/s by an electric field of strength 1.2E5 N/C. What is the force of gravity of the sphere?

    3)How did Benjamin Franklin define a negative charge?

    4) Draw a diagram to show the lines of force around a small positive charge.

    5) Point P is 3.0 cm away from a small object with a positive charge of magnitude 5.0 muC. What is the electric field strength at point P?
    2. Relevant equations

    3. The attempt at a solution
    1) One has to be positive and one has to be negative.

    2) 1.2E5 N/C=Fg/4.8E-14 N
    Fg=5.8E-14 N

    3) He defined it as having more electrons than protons.

    4) positive.jpg

    5) QE=(kQq)/r^2
    E=[(9.0E9)(5.0E-6 C)]/(0.030m)^2
    E= 5.0E7 N/C
  2. jcsd
  3. Jan 3, 2007 #2


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    Staff: Mentor

    In the diagram, remember that the lines of the electric field (and hence the lines of force) originate on + charges and terminate on - charges. How would that change your drawing some?
  4. Jan 3, 2007 #3
    you mean drawing the lines out of the positive charge?
  5. Jan 4, 2007 #4


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    Staff: Mentor


    There would be two cases, with variations on those two cases, right? The first would be a simple diplole, where there are two equal charges spaced apart. What would the E field distribution (and therefore the force vector field) look like for that?

    The second case is a positive charge embedded in an overall E field that is generated by something external (like a positive ion sitting between the plates of a capacitor). How would that change the E field diagram?
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