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: Attractive Force of two charges in water

  1. May 20, 2010 #1
    Two test charges suspended in vacuum attract each other with a force of 1x10^-6 N. What will the attractive force be if the vacuum is replaced with water at 20 C? The permittivity of water at this temperature is 7.07x10^ -10 C^2/N-m^2.

    Fwater = (1/4pi*Ewater)(Q1Q2/r^2)

    Force is in Newtons
    Ewater is the permittivity of water
    Q1 and Q2 are the charges in Coulombs
    r is the separation in meters

    My attempt :(

    I am told that this can be simplified down to the following equation.

    Fwater = K / Fwater

    K is constant, calculated by rolling everything that doesn't change (4pi, the charges, the distance) into one number.

    K = 1/4pi*Ewater

    K = 1/1.256^-1*7.07 x 10^-10 C^2/N-m^2

    K = 1/8.88^-11 C^2/N-m^2

    K = 1.12^-10 C^2/N-m^2

    After finding K is this the correct formula?

    Fwater = (1.12^-10 C^2/N-m^2) / (7.07 x 10^-10 C^2/N-m^2)
    Last edited: May 20, 2010
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted