Oscillating Dipole: E & B Fields Near Source

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    Dipole Oscillating
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Discussion Overview

The discussion centers on the behavior of electric (E) and magnetic (B) fields generated by an oscillating dipole, specifically focusing on the differences between the near field and far field regions. Participants explore the complexities of calculating these fields near the source compared to the simpler far field analysis, referencing relevant texts for deeper understanding.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that the class focused on far field effects, suggesting that the near field behavior may not have been covered due to its complexity.
  • Another participant explains that while the near field equations are more complicated, they can still be solved, and implies that the far field is often studied for its simplicity and clarity in understanding polarization and power distribution.
  • A participant inquires about methods for solving the near field equations, indicating a desire for more detailed guidance.
  • One reply suggests consulting Jackson's E&M text, specifically chapters 8 and 9, for a more thorough explanation of the near field.
  • Another participant describes a simplification approach for calculating fields when the distance between dipole charges is small compared to the distance from the test point, but acknowledges that this simplification breaks down in the near field.
  • There is a clarification that the discussion is specifically about dipole radiation, which may not have been the initial focus.
  • One participant confirms that the difference in distances from the dipole charges must be accounted for in the near field, leading to a more complex problem.
  • A later reply references JD Jackson's text, noting the distinction between the "radiation zone" and the "near zone," where the E field behaves more like that of a static dipole.

Areas of Agreement / Disagreement

Participants generally agree that the near field and far field behaviors of the dipole fields are different, but there is no consensus on the best approach to solve the near field equations, and the discussion remains unresolved regarding specific methodologies.

Contextual Notes

Limitations include the complexity of the near field equations and the potential need for additional assumptions or definitions that have not been fully explored in the discussion.

jc09
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Was studying in class the effects of the E and B fields far from the source and what they looked like, but we failed to discover what happens near the source...Is this because there is no difference or did we just not cover the material
 
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In the near field, the equations are more complicated. For the oscillating dipole, you can still solve them, however. I'm guessing you focused on the far fields because they are simpler and give you a good idea of the distribution of polarization and power radiated.
 
Ok so they are different how would you go about solving them for the near field then?
 
I don't know how much you already know and what sort of explanation would help. But to describe it would take too long here, anyway. If you have a copy of Jackson's E&M text, look in chapters 8 and 9.
 
ok I'll give that book a look thanks
 
If the distance from the test point to one of the charges is r1 and the other charge is r2, when distance separating the dipole charges is significantly less than than r1 and r2, then the charges can be handled as if they were both an equal distance, r, from the test point (i.e. r=r1=r2). This simplifies the calculation. As you consider test points closer to the dipole, the difference in their distances, |r2-r1|, becomes a factor and you can no longer use the single distance r.
 
My apologies - you're looking at dipole radiation.
 
So when we calculated the fields far from the source the distance from each was the same cause the difference between the two was so small but close to the source the distances have to be taken as separate values so more complicated problem yeah?
 
Yeah - at least that's so for analyzing the static dipole. For the dynamic case, (if you have JD Jacksons text on Classical Electrodynamics, see pg 411) he describes the difference between the "radation zone" (relatively far from the dipole) and the "near zone" where the E field predominates. The field in near zone behaves more like the static case.
 

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