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What is the total dipole moment 
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#1
Jun1712, 08:25 AM

P: 1,005

Sometimes I am asked to compute the total dipole moment of a charge configuration. Normally you work with dipole moment per unit volume, so you can find the above by integrating over the entire volume, which is quite easy. I'm curius though, what is the physical interpretation of the total dipole moment of a charge configuration? What does this quantity tell us and is it used in any calculations? Like often you find the total dipole moment to be zero  what does that show us?



#2
Jun1712, 05:15 PM

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P: 5,003

The primary reasons for defining such a quantity are: (1) The dipole contribution to the electrostatic potential can be easily expressed in terms of [itex]\mathbf{p}[/itex] as [tex]V_{\text{dip}}(\textbf{r}) = \frac{1}{4\pi\epsilon_0}\frac{\mathbf{p} \cdot \mathbf{r}}{r^3}[/tex] and this contribution typically dominates at large distances from a distribution with little or no net charge (a very common scenario!) (2) The force, torque and electrostatic energy of as perfect dipole are easily expressed in terms of [itex]\mathbf{p}[/itex] and often make good approximations for calculating the dynamics of a neutral charge distribution, relatively far from it. 


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