Author Topic: Propagation of Electromagnetic Wave  (Read 640270 times)

Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
Re: Propagation of Electromagnetic Wave
« Reply #30 on: April 14, 2009, 12:32:30 am »
You should be able to find the source code (attached file at the top message) now.

borlam

  • Newbie
  • *
  • Posts: 1
Propagation of Electromagnetic Wave
« Reply #31 on: April 22, 2009, 01:28:05 am »
Hello,

If the default (reset) value represents the speed of light in a vacuum, then does this applet let you increase the speed of light?  Also, is it physically possible to have B greater than E?  It seems to me that would only happen if light were slowed to less than 1 m/s.  I read that physicists have slowed it to as little as 17 m/s. Would something bizarre happen to the nature of light if B were greater than E? Or would that not matter from a physics perspective.

I am grateful for your help in my understanding. Thank you.

 


Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
Re: Propagation of Electromagnetic Wave
« Reply #32 on: April 22, 2009, 05:07:24 pm »
Yes. For real electromagnetic wave in vacuum, the speed of light is 3*108m/s.
And the ratio of E/B=v.
There is no way to draw both E and B in the same simulation if the ratio of E/B=c.
And it is also impossible to show the wave proprgate as "REAL speed of light" in the simulation.
This is just a simulation, the purpose is to show the direction of E and the direction of B related to the propogation of the wave.  ;)

wanelson23

  • Newbie
  • *
  • Posts: 1
Re: Propagation of Electromagnetic Wave
« Reply #33 on: November 18, 2009, 04:15:35 pm »
According to your model it appears that the electromagnetic wave is propagating in opposite directions simultaneously and therefore is it not so that the same photon could be detected in two different places at the same time (equal but opposite distances from the origin of the accelerating electron)? And how can the velocity of electromagnetic radiation point in two opposite directions at the same time since by definition a vector can only point in one direction?



Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
Re: Propagation of Electromagnetic Wave
« Reply #34 on: November 18, 2009, 05:13:07 pm »
Actually, if electrons are moving as SHM in an antenna (for example: driven by an AC signal), the generated electromagnetic field should be distributed uniformly in all direction, i.e. EM wave should move in all radial direction (circular wave front moving outward from source).

However, I only draw EM wave in two opposite directions so that it will be easier to find out relation between electric field and magnetic field.

martin030

  • Newbie
  • *
  • Posts: 1
Re: Propagation of Electromagnetic Wave
« Reply #35 on: July 18, 2010, 03:27:34 am »
Thanks!  Nice simulation.

KathieKa

  • Newbie
  • *
  • Posts: 1
    • ao dai
Re: Propagation of Electromagnetic Wave
« Reply #36 on: September 23, 2010, 03:46:57 pm »
Fantastic post cause in my language, i can not find much good source like this.This could aid lots of people find out about this matter. Do you want to incorporate video clips together with these? It could undoubtedly help out. Your reason was spot on and owing to you; I probably won't have to describe everything to my pals. I can simply direct them here. -*-

giant1211

  • Newbie
  • *
  • Posts: 5
Re: Propagation of Electromagnetic Wave
« Reply #37 on: August 01, 2012, 05:28:00 pm »
 It looks like the head of the wave is creating new oscillations as it moves along, and that it is moving faster than the rest of the profile of the wave. Which speed is the speed of light, the head of the wave or the rest of the profile?

Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
Re: Propagation of Electromagnetic Wave
« Reply #38 on: August 01, 2012, 06:01:34 pm »
This siulation simulate a charged particle move in sine-wave y(t)=Y *sin(wt)

It generate wave move in x-direction -which is moving in constant speed (speed of electromagnetic wave or speed of light). 

Do not confuse the speed of charged particle and the speed of the generated wave.

giant1211

  • Newbie
  • *
  • Posts: 5
Re: Propagation of Electromagnetic Wave
« Reply #39 on: August 02, 2012, 12:40:21 am »
But the wave seems to be both generated by the charged particle at the origin and and it also appears to be expanding at the head of the wave. If you were to take the charged particle out of the simulation at any time after t=0, it looks like the wave would still grow larger because the front of the wave is generating it's own oscillations and is moving faster than the rest of the profile. If you look at the simulation with the charged particle in place: after one period T, the wave is growing by 4pi as the both the front end and the back end of the wave seem to expand. This is where I am confused, if the front end were moving at the same speed as the rest of the profile then it would never have the speed to separate from the rest of the profile and expand the wave further. The front end of the wave would always be at the same phase. Thanks for your help!
« Last Edit: August 02, 2012, 12:49:19 am by giant1211 »

Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
Re: Propagation of Electromagnetic Wave
« Reply #40 on: August 03, 2012, 05:49:20 pm »
There is only one charged particle at the origin which is accelerated as sine-wave.
The oscillating charged particle will produce changing electric field, which in term induced magnetic field at the next instance.
The induced oscillating magnetic field re-generate electric field at the near space.
The above process continue and produce the electromagnetic field.

The EM wave move with constant speed in the x-direction in the above simulation. I am sorry that It give you wrong impression and make you confused. Sorry!

giant1211

  • Newbie
  • *
  • Posts: 5
Re: Propagation of Electromagnetic Wave
« Reply #41 on: August 07, 2012, 12:47:17 pm »
Hi there, thank you for your response. I am still a little bit confused. I see that the particle produces a sine wave and emits the B and E fields as they are shown. When I thought of an E&M wave, I thought that the front end of the wave would always be at the same phase. It would be as if you drew a sine wave on a sheet of paper and just carried the sheet of paper in the x direction. And that sheet of paper (the profile of the wave) would travel forward in the x-direction at c. But now with this animation it looks as though the E&B field at the front of the wave are oscillating forward (expanding the profile), followed by the rest of the profile traveling behind. It would be as though I drew a sine wave on a sheet of paper, and continued drawing further on the paper as I walked in space (so that the profile itself is getting larger). Does this make sense? For that reason I'm confused at the two different speeds I see, the one of the entire profile moving and then the one of the front of the wave pulling away from the rest of the profile.

giant1211

  • Newbie
  • *
  • Posts: 5
Re: Propagation of Electromagnetic Wave
« Reply #42 on: August 07, 2012, 01:11:01 pm »
For instance, in this picture (http://universe-review.ca/I13-15-travelingwave.jpg). The front of the wave is at 0 phase and travels like that with the rest of the profile in the x-direction. I know that E&M waves do not necessarily need to start with 0 phase like mechanical waves, but this picture explains how I pictured the E&M waves to travel. The movement of the rest of your profile follows this behavior, it is just the very front of the wave (where it is oscillating the phase it is in) is confusing me. Thank you for helping me understand.
« Last Edit: August 07, 2012, 01:12:51 pm by giant1211 »

giant1211

  • Newbie
  • *
  • Posts: 5
Re: Propagation of Electromagnetic Wave
« Reply #43 on: August 08, 2012, 01:18:17 am »
such as this animation from this video: http://www.youtube.com/watch?v=Ubz-KmCecN8#t=41m05s

Fu-Kwun Hwang

  • Administrator
  • Hero Member
  • *****
  • Posts: 3062
    • Enjoy the fun of physics with simulations
Re: Propagation of Electromagnetic Wave
« Reply #44 on: August 08, 2012, 08:02:58 am »
Thank you for your feedback and information provided!