What Are the Mathematical Foundations of the Dipole Approximation?

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SUMMARY

The dipole approximation is mathematically grounded in the condition that the dipole moment \(d\) is significantly smaller than the distance \(r\) from the dipole to the observation point, expressed as \(d \ll r\). This approximation leads to the relation \(r_1 - r_2 \approx d \cos \theta\), which can be derived using vector addition and Taylor expansion for small values of \(\frac{d}{r}\). The discussion emphasizes that this approximation is not merely a special case but is frequently utilized in physics to simplify calculations involving electric fields and potentials generated by dipoles.

PREREQUISITES
  • Understanding of vector addition and subtraction
  • Familiarity with Taylor series expansion
  • Basic concepts of electric dipoles
  • Knowledge of electric fields and potentials
NEXT STEPS
  • Study the derivation of the dipole moment in electrostatics
  • Learn about Taylor series and their applications in physics
  • Explore the implications of the dipole approximation in electromagnetic theory
  • Investigate other approximations used in classical physics
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Students and professionals in physics, particularly those focusing on electromagnetism, as well as anyone interested in the mathematical foundations of physical approximations.

center o bass
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Homework Statement


I'm referring to http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dipole.html and the approximation r_1 - r_2 \approx = d \cos \theta. I see that it is correct if I draw it up, but I wondered if there were any "more mathematical" ways to see this?

Where does these kind of approximations come from? Is this just a special case or is it often used? I don't think I've seen this kind before.
 
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center o bass said:

Homework Statement


I'm referring to http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dipole.html and the approximation r_1 - r_2 \approx = d \cos \theta. I see that it is correct if I draw it up, but I wondered if there were any "more mathematical" ways to see this?

Where does these kind of approximations come from? Is this just a special case or is it often used? I don't think I've seen this kind before.

The only approximation you need is that d \ll r, i.e. the dipole is very small compared to the distance(s) from its center at which you are interested in measuring the field or potential.

To see how this approximation implies that |\textbf{r}_{+}-\textbf{r}_{-}|\approx d\cos\theta, you simply use the standard rules for vector addition/subtraction and calculate the magnitude of |\textbf{r}_{+}-\textbf{r}_{-}|, then Taylor expand it for small \frac{d}{r}.
 

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