Why Does Dipole Radiation Shift from Radial to Theta Hat Direction?

Click For Summary

Discussion Overview

The discussion revolves around the nature of electric dipole radiation, specifically the transition of the electric field direction from radial (r hat) to theta hat in the context of oscillating dipoles. Participants explore the conceptual understanding of electric fields generated by dipoles, including their behavior in static and dynamic scenarios.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the direction of the electric field from an oscillating dipole, noting that traditional understanding associates electric fields with radial (r hat) directions for point charges.
  • Another participant clarifies that for a physical dipole, the electric field is not purely radial and includes contributions from both the electric and changing magnetic fields, especially when oscillating.
  • It is noted that the static electric field of a dipole has components in theta hat, r hat, and phi hat directions, indicating a more complex field structure than just radial.
  • A participant questions whether the radiation still has an r hat component, suggesting that while it reaches observers from a distance, its dependence on theta is significant.
  • A later reply confirms the previous participant's assertion about the radiation having an r hat component while emphasizing its strong theta dependence.

Areas of Agreement / Disagreement

Participants generally agree that the electric field of a dipole is more complex than a simple radial direction, with multiple components involved. However, there is some uncertainty regarding the exact nature of the radiation and its dependence on the angle.

Contextual Notes

The discussion does not resolve the nuances of how the electric field behaves in different scenarios, particularly in terms of the contributions from static versus oscillating dipoles and the interplay between electric and magnetic fields.

AriAstronomer
Messages
46
Reaction score
1
Hello everyone,
I'm a bit confused about electric dipole radiation. In my E&M book "Intro to Electrodynamics" by David Griffiths, it states that the electric field from an oscillating dipole is in theta hat direction. Mathematically I have the proof as to why in my book, but conceptually I'm having a hard time picturing everything.
Normally, electric field goes radially in r hat direction. Since it is a transverse wave, I picture it like a hand moving a string up and down, and the wave is perpendicular to the hand motion. I don't picture the electric field moving in circles (do they close in on themselves like magnetic field??) around a dipole. What's causing this change from an r hat direction (pointing away from a charge) to theta hat (perpendicular to a charge)?

Ari
 
Science news on Phys.org
AriAstronomer said:
Normally, electric field goes radially in r hat direction.

That's for a single point charge. Consider a "physical" dipole, which consists of two opposite charges with equal magnitude, separated by a short distance. Even for a static dipole (not oscillating) the net E field is radial only along the dipole axis.

With an oscillating dipole, you also have contributions to the E field that are related to the changing magnetic field.
 
jtbell said:
That's for a single point charge. Consider a "physical" dipole, which consists of two opposite charges with equal magnitude, separated by a short distance. Even for a static dipole (not oscillating) the net E field is radial only along the dipole axis.

With an oscillating dipole, you also have contributions to the E field that are related to the changing magnetic field.

In other words, the static electric field of a dipole does not go around in a circle. It as a theta-hat component, but it has r-hat and phi-hat components as well.
 
But it still radiates in the r hat direction doesn't it? I mean the fact that it reaches you from some distant point means it must have an r hat component, but I guess the point is that it's highly theta dependent?
 
AriAstronomer said:
But it still radiates in the r hat direction doesn't it? I mean the fact that it reaches you from some distant point means it must have an r hat component, but I guess the point is that it's highly theta dependent?

Yes, exactly right.
 

Similar threads

Graduate Origin of Hertzian dipole radiation
  • · Replies 21 ·
Replies
21
Views
2K
Graduate Energy-to-angular momentum ratio in EM v. gravity quadrupole radiation
  • · Replies 0 ·
Replies
0
Views
1K
Torque that a grounded infinite sheet exerts on a dipole
  • · Replies 11 ·
Replies
11
Views
2K
Graduate Relation of EM radiation equation to radioactive decay
  • · Replies 3 ·
Replies
3
Views
2K
Effect of different magnetic fields on a magnetic dipole
  • · Replies 25 ·
Replies
25
Views
2K
Why is a current ring approx a magnetic dipole from very far off?
  • · Replies 7 ·
Replies
7
Views
2K
MIT OCW, 8.02 Electromagnetism: Potential for an Electric Dipole
  • · Replies 1 ·
Replies
1
Views
3K
Understanding work in translation and rotation of a magnetic dipole
  • · Replies 1 ·
Replies
1
Views
2K
High School Why does charge oscillate in an electric dipole antenna?
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Confusion on Source of EM Radiation? (segment Serway)
  • · Replies 2 ·
Replies
2
Views
2K