# NTNUJAVA: Virtual Physics Laboratory: Enjoy the fun of Physics

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• Propagation of Electromagnetic Wave by:at 2004/01/29 22:46

You are welcomed to check out EM circular polarized wave or polarizer + EM circular/linear polarized wave

This java applet shows how the electric field, the magnetic field and the wave vector inter-relate as the electromagnetic wave propagates through space.

 Red arrow Blue arrow Green arrow Electric field E Magnetic field B Velocity vector of wave V fixed Click near tip of B then drag the mouse to change the velocity of the EM wave keep E + V X B = 0

Press the start Button to start the animation.

The electromagnetic wave propagates in the opposite direction (from the origin).
Press the LEFT mouse button to pause the animation. Press it again to resume.
Press the RIGHT mouse button and drag the mouse to change the viewing angle.
Right click near the origin to move it.

T-field is the period (in seconds) [or 'fractions of a second' if referring to less than one second].
The speed of propagation remains constant but the period may vary ...(Thanks to Michael De Groot for his suggestion).
Press the Reset button to reset.

Thank Mark Servis for correction in the code (Oct. 8, 2001)

The following is a youtube movie about electromagnetic wave

See 42 replies click

1. topic35 by:at 2004/01/30 08:40Subject: EM wave Applet Date: Mon, 01 Sep 1997 17:34:13 -0700 From: "Sunil K. David" <davids@cookman.edu> Organization: Bethune-Cookman College To: hwang@phy03.phy.ntnu.edu.tw, rao@cookman.edu Hi: You have made my job quite simple in showing the prop. of EM wave for my class. Congratulations. Great applet. Goodluck, Bye, Sunil K. David, M.Sc., M.Sc. Ph.D. Assistant Professor of Physics

2. topic35 by:at 2004/01/30 12:38Subject: E&M Waves Date: Tue, 09 Mar 1999 00:34:41 -0800 From: Chun-Te Peter Wu <peterw@ucla.edu> To: hwang@phy03.phy.ntnu.edu.tw Hi Professor, I visited the your E&M website and I am very impressed with the animation of the E&M waves. I especially liked the rotations of axis. Good Job -Peter

3. topic35 by:at 2004/01/30 12:42Subject: Re: about your page in http://iswww4.moe.edu......emwave.html Date: Tue, 23 Mar 1999 16:19:43 -800 From: jflores1@upb.edu To: Fu-Kwun Hwang <hwang@phy03.phy.ntnu.edu.tw> hi.. thanks 4 the help my teacher liked the animation...!!! and the rest of the class too..!! once again thanks http://www.upb.edu

4. topic35 by:at 2004/01/30 13:53Subject: Electromagnetic wave propogation Date: Thu, 21 Oct 1999 15:45:24 +0100 From: "Arif Zubairi" <zubairi@nortelnetworks.com> To: "'hwang@phy03.phy.ntnu.edu.tw'" <hwang@phy03.phy.ntnu.edu.tw> Hi I was recently scouring the net looking for a suitable picture to demonstrate the orthogonal mode of an electromagnetic wave in an optical fibre for a presentation on polarisation dispersion (my artistic skills are nil). I came across your moving Java applet description of an EM wave and was suitably impressed as its exactly the type of picture I'm looking for. I was wondering whether you might have still pictures of the sort that I might be able to post in a Powerpoint presentation. If you do I would be much obliged. Thanks Regards Arif Zubairi Product Engineering Nortel Networks External: % 0181 945 3720 ESN: % 730 3720 E-mail: ) zubairi@nortelnetworks.com -------------------------------------------------------------------------------- thanks kindly. Much appreciated.

5. topic35 by:at 2004/01/30 18:01Date: Mon, 22 Jan 2001 22:03:52 -0500 From: Katrin Kneipp <KatrinKneipp@compuserve.com> Subject: Your em wave animation Sender: Katrin Kneipp <KatrinKneipp@compuserve.com> To: "H.Wang" <hwang@phy03.phy.ntnu.edu.tw> Dear collesgue, I'm writing to kindlly ask you for setting a link to your em Wave animati= on from the home page of my Single Molecule Spectroscopy course, MIT course 6.975 Spring 2001. http://ourworld.compuserve.com/Homepages/KatrinKneipp/6975.htm Many thanks and best regards, Katrin Kneipp *********************************** Katrin Kneipp Rockefeller Mauze Visiting Professor Massachusetts Institute of Technology Department of Physics Department of Electrical Engineering and Computer Science G. R. Harrison Spectroscopy Laboratory, Room 6-014 77 Massachusetts Avenue, Cambridge MA 02139-4307 Phone (617) 253 3378, Fax (617) 253 4513 e-mail:kneipp@usa.net

6. topic35 by:at 2004/05/05 07:47Mr. Hwang: In your animated propagation of EM waves, what is the green dot? electrons have charge photons have discrete enery which do not vary during propagation light waves are compsed of photons(not electrons or positrons) photons travel in straight lines Are your graphics about electon emision?

7. topic35 by:at 2004/05/06 08:30It could represent an oscillating charge (if this is the case: the simulation only show one of the possible EM-wave)

8. a question by:at 2004/05/07 00:51using a length of open-circuited transmission line, we can design a tuning stub to match a 75ohm line to (150-j75)ohm load. What is the distance from the load to place the line, and legth of open circuited line. Do you know any method to solve this, other than smith's chart? of what practical relevance is the design of matching stubs? what factors would dictate your selection of an open-circuited vs short-circuited? Thanks, spectnas

9. oh by:at 2004/09/15 05:13[b:63c7c331eb]Beautiful![/b:63c7c331eb] :shock: What a beautiful animation. To those who are curretly studying Electromagnetic Waves - like Í'm doing - this is a spetacular way of seeing how those fields propagates with a beam of light! VF

10. topic35 by:at 2005/07/20 11:44David Paraschuk : > Hello, > > I was just running though some of your excellent java applets and I have a question concerning the propagation of EM waves. Every text resource or web resource depicts the E and B field components as reaching a maximum and minimum in phase. Yet the theory of Maxwell clearly indicates that the rate of field change in the mutual self-induction cycle is what is important, ( E∝ £GB/£Gt ). I think during the wave cycle when the E field is a maximum, the rate of change temporarily falls to zero and the the B field at that instant would be zero. The opposite would be true for the generation of the E field by a changing B field. Therefore a maximum E and B field can never be produced together in time and space. > > If this follows then the traditional drawings of the EM waves are incorrect and the wave peaks should be out of phase by 180 degrees! > > If you could briefly comment on this thinking I would be in your debt. Thank you. It is the gradient of E in the space coordinate is proportion the rate of change in B field. i.e. grad E = - dB/dt It is different from E= -dB/dt (E and B should be out of phace) So E and B do not necessary to be out of phase. They can be in phase or out of phase or other case (phase different not 90 degree).

11. topic35 by:at 2006/01/14 07:07shouldnt it be B X V = E instead of V X B = E ??

12. topic35 by:at 2006/01/14 17:19Sorry! It is corrected. It should be EXB=V or VXE =B or BXV=E ! :-)

13. topic35 by:at 2006/03/02 06:03I want to get file related to EM Waves for offline use in my classroom. Thank you. Helder de F. e Paula

14. topic35 by:at 2006/03/02 09:52Login to the forum and press "GET APPLET FILES" button near the end of the first message.

15. topic35 by:at 2006/08/26 14:46great job thanks for making physics so understandable to students.it really helps if we can show them what really happens then talking about what happens. congratulations. great combination of physics and programming.

16. Re: Propagation of Electromagnetic Wave by:ferro638at 2007/05/07 02:42Hello!

Excellent animation! I'm doing a PowerPoint presentation about this subject. Is it possible to put this animation in my PoerPoint presentation, to be shown in a computer WITHOUT internet? If so, how can I do it?

Thanks.

17. Re: Propagation of Electromagnetic Wave by:hwangat 2007/05/08 00:38As far as I know, java applets can not be embed into powerpoint.
However, you can download out applet and add a link in powerpoint to open the web page which contains java applets.

18. Re: Propagation of Electromagnetic Wave by:NightAngelat 2007/07/05 01:18hihi... can i have the source code? i was download the file, it is appear in .class file. is it possible view in source code from the .class file?

19. Re: Propagation of Electromagnetic Wave by:hwangat 2007/07/10 05:58You should have received source code now.

20. Re: Propagation of Electromagnetic Wave by:kontellisat 2008/02/06 19:04Hello Mr Huang and the rest of your team.
Congratulations for the great job you make.
I'm Kontellis George a teacher of Physics at 3rd Lyceum of Mytilini Greece.
I must thank you for the exciting Applets you have. Many topics of my teachings are much easier to teach with them.
I have two questions about EM waves.
1.  When EM waves transport inside an object is E/B equal with 300000000m/s or smaller?
2.  Near the antenna the two fields seem to have a phase difference of 90 but at a long distance their phase difference become zero. Why is that?
Thank you
George Kontellis
kontellis@sch.gr

21. Re: Propagation of Electromagnetic Wave by:hwangat 2008/02/07 00:331. E/B is the speed of the EM wave and the speed of EM wave is near c=3*10[sup]8[/sup]m/s in vacuum.
But the speed is reduced to c/n when in an object, where n is the refraction index for that EM wave.
2. Could you explain why there is a 90 degree difference in phase for E/M wave  near the antenna?

22. Re: Propagation of Electromagnetic Wave by:oktariniat 2008/08/10 20:57i can`t use it offline
but it can`t work well...
no picture showned

23. Re: Propagation of Electromagnetic Wave by:hwangat 2008/08/10 22:18What did you do with the downloaded file?
Did you unzip the file and open emWave.html with your browser?
I just tried it and it works fine with my browser.

24. Re: Propagation of Electromagnetic Wave by:hwangat 2008/08/11 14:28I just created an EJS version for the same simulation.

The speed of the electromagnetic wave depend on the Electric field E and magnetic field B.
v=E/B
For the same material, the ratio should be fixed.
If only one of them is changed, it mean wave traveling in different material (index of refraction is shown in the simulation).

25. Re: Propagation of Electromagnetic Wave by:Prashat 2009/03/21 14:33when photons have no charge then how time varying electric and magnetic fields generate?

26. Re: Propagation of Electromagnetic Wave by:hwangat 2009/03/21 17:54[u]Photon[/u] and [u]EM wave[/u] are two different [u]models[/u] (particle vs wave) to describe light.
You can check out modern physics textbook for related information.

27. Re: Propagation of Electromagnetic Wave by:maxrkat 2009/04/13 23:55Hi! Hwang
I very like your programing. I want to see source code java. I'm making project about electromagnetics.
please send me source code java  topic Electromagnetics
Thanks
Contact me : trcaoky@yahoo.com :)

28. Re: Propagation of Electromagnetic Wave by:hwangat 2009/04/14 00:32You should be able to find the source code (attached file at the top message) now.

29. Propagation of Electromagnetic Wave by:borlamat 2009/04/22 01:28Hello,

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.

30. Re: Propagation of Electromagnetic Wave by:hwangat 2009/04/22 17:07Yes. For real electromagnetic wave in vacuum, the speed of light is 3*10[sup]8[/sup]m/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.  ;)

31. Re: Propagation of Electromagnetic Wave by:wanelson23at 2009/11/18 16:15According 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?

32. Re: Propagation of Electromagnetic Wave by:hwangat 2009/11/18 17:13Actually, 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.

33. Re: Propagation of Electromagnetic Wave by:martin030at 2010/07/18 03:27Thanks!  Nice simulation.

34. Re: Propagation of Electromagnetic Wave by:KathieKaat 2010/09/23 15:46Fantastic 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.  -*-

35. Re: Propagation of Electromagnetic Wave by:giant1211at 2012/08/01 17:28 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?

36. Re: Propagation of Electromagnetic Wave by:hwangat 2012/08/01 18:01This 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.

37. Re: Propagation of Electromagnetic Wave by:giant1211at 2012/08/02 00:40But 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!

38. Re: Propagation of Electromagnetic Wave by:hwangat 2012/08/03 17:49There 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!

39. Re: Propagation of Electromagnetic Wave by:giant1211at 2012/08/07 12:47Hi 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.

40. Re: Propagation of Electromagnetic Wave by:giant1211at 2012/08/07 13:11For 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.

41. Re: Propagation of Electromagnetic Wave by:giant1211at 2012/08/08 01:18such as this animation from this video: http://www.youtube.com/watch?v=Ubz-KmCecN8#t=41m05s

42. Re: Propagation of Electromagnetic Wave by:hwangat 2012/08/08 08:02Thank you for your feedback and information provided!