# Net force between two dipoles

1. Sep 7, 2008

### kjintonic

1. The problem statement, all variables and given/known data
Two identical dipoles, each of charge q and seperation a, are a distance x apart, as shown in Fig. By considering forces between pairs of charges in the different dipoles, calculate the net force between the dipoles. Show that, in the limit a<<x, the force has magnitude
6kp^2/x^4, where p=qa is the dipole moment.

2. Relevant equations
E=2kp/x^3

3. The attempt at a solution
I have no idea where to start T^T

2. Sep 7, 2008

### Redbelly98

Staff Emeritus
They say to calculate forces between pairs of individual charges.

Which equation gives the force between two charges?

3. Sep 7, 2008

### kjintonic

I really don't know... I am a 11th grader and I'm asked to do university stuff;;

oops i forgot the diagram

----- (- +) ---------------------------------(- +)----
--------a--------------------x-----------------a

EDIT: You mean kq1q2/r^2 ??

Last edited: Sep 7, 2008
4. Sep 7, 2008

### kjintonic

K now I understand that you have to use coulomb's law but how on earth do i find q of one dipole???

5. Sep 7, 2008

### Redbelly98

Staff Emeritus
Yes, use Coulomb's law.

Just leave the charge as q and work through the algebra.