1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Maximum electric force felt by the raindrop

  1. Sep 29, 2011 #1
    Suppose 2 drops with equal charge q are on the x axis at x=+-a. Find the maximum electric force felt by a third drop with charge Q at an arbitrary point on the y axis.

    from the symmetry we can deduce that the x components cancel and the net force is in the y direction. the y component is same for both charges.

    I used Coulomb's Law to get the equation

    F=2((kqQ)/a2+y2)(y/sqrt(a2+y2) j(hat)

    =(2kqQy)/(a2+y2)3/2 j(hat)

    I know that the next step is to find the y value for which the force is maximized, however I'm not too sure on how to do that. I thought maybe the y is max when the charges a are at the origin, but I don't think that the charges could be moved over to the origin for this calculation.

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



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 29, 2011 #2

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    You're right. You can't move the charges on the x-axis; or mathematically speaking, a is a constant. What you can do is move the third charge, that is, vary y, to maximize |F(y)|.
     
  4. Sep 29, 2011 #3
    hmm....

    so since the length from the q charge to the Q charge is inversely proportional to the force felt by Q (1/y), the closer Q is to both q's, the more force it experiences. But if it was the lined up with them on the x axis, the net force would be 0. So, do I need to make it as close to the origin as possible? And would other equations, such as F=qE need to be incorporated to solve for y?

    thanks for helping me
     
  5. Sep 29, 2011 #4

    vela

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Education Advisor

    As close to the origin as possible would be at the origin, where, you have already noted, the force is 0. If Q is very far away, again the force is essentially 0. So the maxima occur somewhere in between.

    You already have the expression for the force. Just find where it's attains a maximum. This is a math problem now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Maximum electric force felt by the raindrop
Loading...