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

[AriAstronomer]

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

 

[jtbell]

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.

 

[Rap]

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.

 

[AriAstronomer]

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?

 

[Rap]

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.