Electric Dipoles: Visualizing Oscillating Dipoles and Traveling Waves

At this point we have discussed stationary dipoles and oscillating dipoles. Now we need to take a bit of time to visually understand how the field radiates away from a dipole in the form of a propagates wave.

For this exercise, navigate to an interactive dipole simulation. Change the settings in the tool-bar at the top of the page to:

Dipoles: Choose "Half Wave Dipole (λ/2)"
3D-View: Choose "3D with Line Graphs"
Regions: Choose "ca. 4 Lamda"
Nonstop: Choose "NONSTOP"

You should get something that looks like this

Dipole Interactive Simulation

In the upper left octant, we see the dipole field amplitude i.e., where the is radiation is stronger and where it is weaker.

In the upper right octant, we see the electric field generated by the oscillating dipole.

Remember that electric field lines emanate from positive charges and terminate on negative charges so we see some field lines pointing up and some pointing down, the direction depending on the time they were 'made'. We also see the 1/r dependence of the field as the vectors get smaller the farther away from the dipole they are.

Now, this is happening in all directions except the direction of dipole oscillation, that's the sin(θ), term again, so you have to imagine the electric field lines symmetrically rotated around the central axis with toroidal symmetry. The sin(θ) term also means that the emission is strongest 90^o away from the dipole direction.

We have a few more things to do in this module but before we move on, I want to show you another animation.

Single Dipole Emitter

In this animation (and all the ones to follow), a plane wave is incident from the left, traveling toward the right
The 'Total Wave' is plotted in the left panel and is the superposition of the incident plane wave and the light generated from (in this case) a single dipole
The right panel is only the Scattered Field. This is the field generated by (in this case) a single dipole