August 04, 2024, 04:18:28 PM
Forum Rules: Read This Before Posting

Topic: intermolecular farces: dipole-dipole interaction  (Read 1979 times)

0 Members and 1 Guest are viewing this topic.

• Full Member
• Posts: 427
• Mole Snacks: +1/-0
intermolecular farces: dipole-dipole interaction
« on: April 01, 2016, 05:49:08 AM »
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,θ12,φ) = -  (μ1μ2) / (4pi ε0ε r3 )   * [2cosθ1cosθ2 - sinθ1sinθ2cosφ ]

In the common situation we have:
E(r,0,0,φ)= -2μ1μ2/4pi ε0ε r3

(case where the two dipole are parallel and in the same verse)

THEN it uses this formula:

E= μ1μ2 f(θ) / 4piε r3
f(θ)= 1-cos3θ

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= μ1μ2  / 4piε r3* 1   -  μ1μ2  / 4piε r3* (3*1)
E= -2 μ1μ2  / 4piε r3

Thanks