Question on EM waves

Question

Every high school student knows that visible light is a form of electromagnetic radiation according to the classical electromagnetism i.e. two alternating, perpendicular fields propagating in space. My question is:

Suppose you have a charged particle in space, and this particle starts to perform a SHM in one specific direction, ( call it the $ x $ direction) and, suppose, that the frequency of this SHM coincides with the frequency of the red light (~750mm). What would a observer nearby see in the $ x $ direction? What would a observer see in any different direction? It would be as if someone lighted up a red lamp in space, or just a light ray in the $x$ direction and darkness in the others?

Thanks in advance.

Answer 1

What would a observer nearby see in the x direction? What would a observer see in any different direction? It would be as if someone lighted up a red lamp in space, or just a light ray in the x direction and darkness in the others?

A charged particle oscillating in x direction will produce a donut shaped radiation diagram, similar to a dipole antenna. The cross-section of the diagram is shown below.

The blue vectors indicate the direction of EM propagation, while their magnitude indicates the magnitude of radiation in that direction. You can see that the maximum radiation is in the equatorial plane of a dipole , while radiation in x direction is zero.

The dipole produces a polarized EM wave with E-field vectors lying in the vertical planes containing the dipole. As shown on the diagram, the direction of E-field vectors (red) is normal to the direction of wave propagation.

So, if the oscillation of the charge was at a visible light frequency, the observer would see maximum light looking from the sides, no light looking from above or below along x axis and something in between looking from any other direction.

Answer 2

Well charged particles are capable of emitting electromagnetic radiation at a specific frequency of oscillation, but take note, this only occurs when the magnetic and electric field surrounding the particle are perpendicular to each other. The charged particle may be moving at the frequency of red light but no sparks nor splash of red light will be seen when there exist an angle other than 90.