Hi!!!

I have some doubt about the expression of the dipole-dipole interaction because my textbook uses two different formulas and I don't understand why/the difference

The first expression that uses for a dipole-dipole interaction is:

E(r,θ

_{1},θ

_{2},φ) = - (μ

_{1}μ

_{2}) / (4pi ε

_{0}ε r

^{3} ) * [2cosθ

_{1}cosθ

_{2} - sinθ

_{1}sinθ

_{2}cosφ ]

In the common situation we have:

E(r,0,0,φ)= -2μ

_{1}μ

_{2}/4pi ε

_{0}ε r

^{3}(case where the two dipole are parallel and in the same verse)

THEN it uses this formula:

E= μ

_{1}μ

_{2} f(θ) / 4piε r

^{3}f(θ)= 1-cos

^{3}θ

What is the difference between these 2 formulas??

And in the second one what is the angle θ ??

And this two formula,in the end,take at the same result?

For example I think that if θ=0pi in the second formula I get:

E= μ

_{1}μ

_{2} / 4piε r

^{3}* 1 - μ

_{1}μ

_{2} / 4piε r

^{3}* (3*1)

E= -2 μ

_{1}μ

_{2} / 4piε r

^{3}Thanks