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Homework Help: Coulomb's law hw question, please help

  1. Jul 27, 2014 #1
    q1= 2microC and q2=-4microC they are on a straight line 5.0 cm away from each other.

    a)find the magnitude of the net force on charge q2 due to q1
    b) in what direction will the net force acting on charge q2 due to q1 be directed
    c)what is the magnitude and direction of the electric field at a point located 5 cm directly below charge q1
    d)what is the magnitude of the electric potential located 5 cm directly below charge q1

    I'm confused on what to do for only two points. Any help is appreciated and please explain so I can try to get an understanding

    for A) i got 28.8 N and B) the forces will attract. not sure if those are correct
  2. jcsd
  3. Jul 27, 2014 #2


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    a) Looks fine.

    b) Indeed the forces attract. On a free body diagram, which way would the force ##\vec F_{12}## point, given an arbitrary coordinate axis placed at ##q_1##?

    c) How do you calculate the electric field at a point, due to a point charge? Hint: Draw a free body diagram for this.
    Last edited: Jul 27, 2014
  4. Jul 27, 2014 #3
    This is what I came up with, it doesn't seem correct to me, but I'm not sure where I went wrong

    Attached Files:

  5. Jul 27, 2014 #4


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    You need to sum the components of the electric field of ##\vec E_1## and ##\vec E_2##.

    What about the direction? Draw ##\vec E_{net_x}## and ##\vec E_{net_y}## head to tail and apply ##tan(\theta) = \frac{E_{net_y}}{E_{net_x}}##.

    d) Same deal as c) pretty much, except potential is used instead of the electric field.
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