Arrange two electric dipoles with dipole moments qd 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 r4.
The Attempt at a Solution
So in my first attempt, all I did was solve the dipole moment eqn for q, (q1=p1/d, q2=-p2/d) and plug that into Coulomb's law so that you get F= -(p1p2/d2)/(4(pi)(eps0)r2)
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 r4 in the denominator which I think then proves that the force falls off at r4.
Is this assumption correct? What is the difference between r and d?