https://www.reddit.com/r/AskPhysics/comments/18reodh/two_questions_about_light_waves/
created by Jeff-Root on 26/12/2023 at 18:30 UTC
4 upvotes, 7 top-level comments (showing 7)
I've read that light waves are transverse waves and that they are sinusoidal. To what extent are these assertions accurate?
Comment by gerglo at 26/12/2023 at 18:45 UTC*
6 upvotes, 3 direct replies
The first is true in ~~vacuum~~ free space (and more generally in linear media). The second is not true: unconfined electromagnetic waves can have any waveform.
Comment by agaminon22 at 26/12/2023 at 18:57 UTC
4 upvotes, 1 direct replies
Neither is generally true. Waves in guiding structures (for example, optical fibers) can have components in the direction of propagation as a simple example. Look up TE, TM and hybrid modes. The second one is also not true, the waveform can be completely arbitrary. Also, at the end of the day what you can measure is the intensity distribution, which for a sinusoidal wave is basically constant (as long as the frequency is high enough).
Comment by James_James_85 at 26/12/2023 at 20:58 UTC
2 upvotes, 1 direct replies
The form of the light waves depends on the motion of the charged particles that generates them. If it's a regular/orderly motion, the light waves will be clean/sinusoidal. Else they'd be messy.
I highly recommend you watch this[1] if you're interested, it simulates the propagation of waves in the EM field with beautiful animations.
1: https://youtu.be/aXRTczANuIs?si=no8fKn_9Y1jQaB1y
Comment by Irrasible at 26/12/2023 at 22:50 UTC
0 upvotes, 1 direct replies
Forget photons. They do not have a magnetic field or an electric field. They are responsible for the actions that used to be attributed to the classical electromagnetic field.
As for the classical EM field, it is easier to answer your question by considering the potentials.
That leaves *gradient* {φ} as a term that might cause **E** to not be perpendicular to **H**.
The scaler electric potential, φ, is determined entirely by charge distributions. However, the universe is or appears to be essentially neutral. So, out in free space, far away from matter, φ~0 and *gradient* {φ} →0. Thus, out in free space, **E**●**H**=0.
So, when can *gradient* {φ} ≠ 0? When you are near stuff. Near a dipole antenna, *gradient* {φ} can be very strong. It can also be non-zero in or near a waveguide.
Comment by [deleted] at 29/12/2023 at 01:32 UTC
1 upvotes, 0 direct replies
They can depart from being sinusoidal, and the angle between the electric and magnetic components may depart from 90 degrees, depending on polarization and the influence of the medium, if any.
Comment by Jeff-Root at 29/12/2023 at 11:57 UTC
1 upvotes, 0 direct replies
Is this accurate?
Light has wave properties. As seen by an inertial observer, the waveform is determined by the accelerations of the electric charges giving rise to the light.
So an electric charge which is accelerating in harmonic oscillations emits light with sinusoidal waveform.
I want to depict a typical photon as perpendicular sine waves in phase with equal amplitude, representing the changing electric and magnetic field strength as the photon passes through space.
As far as I know, the only thing different about this proposed diagram from scores of others I've seen is that I am explicitly saying that the diagram represents a single photon.
Would anything be wrong or misleading about that?
Comment by Jeff-Root at 29/12/2023 at 11:59 UTC
1 upvotes, 0 direct replies
In another thread a few months ago, it was suggested or implied that a photon might not be an indivisible entity. It might be possible to chop a photon in two, and both resulting photons could be detected and measured. Is this a real possibility? It contradicts what I had believed, but seems plausible.