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Homework Help: Find the dielectric constant of the medium?

  1. Apr 4, 2013 #1
    1. The problem statement, all variables and given/known data
    Two point charges a distance d apart in free space exert a force of 1.4∗10^−4 [N]. When the free space is replaced by a homogeneous dielectric medium, the force become .9∗10^−4 [N]. What is the dielectric constant ϵr of the medium?

    2. Relevant equations

    3. The attempt at a solution
    I have been staring at this problem for awhile. I can only think of using E=F/Q. But the problem is this only applies to free space and I do not know Q. So I am not sure where to start to compare the free space and medium.
  2. jcsd
  3. Apr 4, 2013 #2
    The coulombic force in free space is k.q1.q2/r^2. In a medium, the value of k changes to k/dielectric constant. Now try to solve the question. :D
    Hint : Compare the 2 values of electrostatic force.
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