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Homework Help: Physics-electric charge(coulomb's law)

  1. Jul 26, 2014 #1
    The question is this:
    Calculate the position on the line joining 2 charges 1.67 uC and -0.6uC situated 0.4m apart where a third charge q does not experience any force?


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  2. jcsd
  3. Jul 26, 2014 #2


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    Homework Helper

    The reason it comes out as a quadratic equation because there are two places that satisfy the problem
    (You can place it at a certain distance to the left of the charges, or a certain distance to the right of the charges.)

    The reason your quadratic was imaginary is because you set up the initial equation wrong.

    You want [itex]F_1+F_2=0[/itex] and therefore [itex]F_1=-F_2[/itex] (Whereas you wrote "[itex]F_1=F_2[/itex]" without the negative sign)

    In the future, it would be very helpful if you typed out your thoughts in the thread. The reason is that it can sometimes be difficult to read off of a picture. (And I almost didn't even notice that there were words in your picture!) Thank you :)
  4. Jul 26, 2014 #3
    It did not give any solution
  5. Jul 26, 2014 #4
    Let the point at which q[itex]_{3}[/itex] does not experience any force be x.(Let this x be measured from q[itex]_{1}[/itex])
    Not distance of that specific point from q[itex]_{2}[/itex]=(0.4-x)
    Since net force on q[itex]_{3 }[/itex] is zero so

    Put the values and get the answer.
  6. Jul 26, 2014 #5
    It does give a solution. Please re-check your calculations, what equation do you get after applying the correction Nathanael suggested?
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