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!

Electric force magnitude of NH3

  1. Jan 20, 2010 #1
    1. The problem statement, all variables and given/known data

    The structure of NH3 the molecule is approximately that of an equilateral tetrahedron, with three H+ ions forming the base and an N3− ion at the apex of the tetrahedron. The length of each side is 1.64 10-10 m. Calculate the magnitude of the electric force that acts on each ion. (Let the H+ ions be in the x-y plane with H1 at (0, 0, 0), H2 at (a, 0, 0), and H3 (a/2,(a*sqrt(3))/2,0), and the N is at (a/2,a/(sqrt(3)*2),a*sqrt(2/3))

    where a = 1.64 10-10 m. To simplify our calculations we'll set (ke^2)/a^2 = C = 8.56 10^-9 N. Use the following variable as necessary : C.)

    Find the magnitude of force on H1

    2. Relevant equations
    (K* lq1*q2l)/r^2=F(E)

    3. The attempt at a solution

    First of all after sketching a little diagram I concluded that the force of h2 on h1 was < - ,0,0>, h3 on h1 <-,-,0), and N on h1 <+,+,+>. Made these conclusions by looking at the direction the force would be. In the end I used these signs to give my magnitudes direction in order to add the vectors.

    I found the distance between them all from h1 by using the distance formula. They have the same distance which is "a".

    Then I set up triangles for them all except the first one because it is pushed straight down the x axis.

    So for h2 on h1 I got (Ke^(2))/a^(2)<-1,0,0>

    For h3 on h1 I got a triangle with a side in the x direction with a length of a/2 and the side in the y was (a*sqrt(3))/2. So I used tan(o/a)=30 degrees.

    So I took the sin and cos of 30, and figured I needed to multiply my force by 1/2 to get the x comp, and root3 over 2 to get my y comp.
    (Ke^(2))/a^(2)<-.5,-sqrt(3)/2,0>


    Then for my N on h1 I did the same process and got

    (3ke^2)/a^2<sqrt(3)/2,.5,.8164965809>

    Then I added all my vectors together.

    <(3^(3/2)-1-.5, 1.5-sqrt(3)/2, 3(.8164965809)>


    The x and y component are apparently supposed to both be zero but I don't get them cancelling out.

    Does anyone see where my error occured? Or at least can anyone tell me if I am taking the right steps.
     
    Last edited: Jan 20, 2010
  2. jcsd
  3. Jan 20, 2010 #2
    I cleaned up my post a little bit. so hopefully it is understandable now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Electric force magnitude of NH3
Loading...