1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Force between two charged particles at a distance question, help please?

  1. Oct 14, 2014 #1
    1. The problem statement, all variables and given/known data

    Two small electrically charged objects are placed 6 centimeters (cm) apart, where they exert a force of 8 N on each other. How far apart must they be placed in order to exert a force of 1 N on each other? Assuming that the charges on the two objects are equal, what is the charge?

    2. Relevant equations

    F = q1 x q2 / d^2

    3. The attempt at a solution

    This questions seems to be simple to me, yet, I don't know why I'm so stuck...so....here is my reasoning:

    If at 6 cm, the force = 8N and we want to find out what the distance between the charged particles is when the force between them is 1N...I'm assuming that they would have to be further apart so the force between them decreases by a magnitude of 8 times....and since the force weakens as the distance between the particles is squared then: square root of 8 = 2.82 x 6 cm = 16.97 cm? (I'm not sure if that is correct) and then to find the charge on the particles...I'm at a loss...but assume that if the above calculation is correct; I could substitute the values into the equation and clear for q^2? Thanks in advance for any help you can give me!
  2. jcsd
  3. Oct 14, 2014 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Don't forget the constant k (Coulomb's constant).


    This problem has nothing really to do with the first part. Just pick one of the distances, plug the given data into Coulomb's law, and solve for the charge. Careful with units! And don't forget that constant.
  4. Oct 14, 2014 #3
    Hello Doc Al,

    Thanks for your reply and help....so...would this be correct?

    F=9x10^9 * q1 x q2 / d^2
    1N=9x10^9 * q^2 / 0.1697m^2
    q=√0.0288m x 1N / 9x10^9
    q=1.78 x 10^-6 Coulombs

    Thanks so much!
  5. Oct 14, 2014 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Looks good!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted