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## Homework Statement

Arrange two electric dipoles with dipole moments

*q*

**d**nose to tail at a distance

**r**

*(r >> d)*along a line including their axis. Use Coulomb's law to show that the force between them varies as r

^{4}.

## Homework Equations

## The Attempt at a Solution

So in my first attempt, all I did was solve the dipole moment eqn for q, (q

_{1}=p

_{1}/d, q

_{2}=-p

_{2}/d) and plug that into Coulomb's law so that you get F= -(p

_{1}p

_{2}/d

^{2})/(4(pi)(eps

_{0})r

^{2})

Now the part where I am confused is the difference between r and d. If they are just different ways of describing the same thing, then I would get r

^{4}in the denominator which I think then proves that the force falls off at r

^{4}.

Is this assumption correct? What is the difference between r and d?