EM waves

  • #1
8
2

Main Question or Discussion Point

Why are electric and magnetic fields in an electromagnetic wave in phase? Can somebody please explain that???
 

Answers and Replies

  • #2
941
394
I'd imagine it has to do with the fact that the electric field created is directly proportional to the rate of change of the magnetic field, and the magnetic created is directly proportional to the rate of change of the electric field, but I feel this is a very hand-wavy answer, and I await a more knowledgeable person to provide a more thorough answer.
 
  • #3
8
2
I think that it has got something to do with Faraday's Law and Ampere's law. But as you said, let's wait for somebody to give a robust answer.
 
  • #4
blue_leaf77
Science Advisor
Homework Helper
2,629
784
In general E and B field are not always in phase. They are in phase if there's no net free charge flow in the medium through which the wave propagates, example of such media are dielectric and vacuum (this one not really a medium though). If there is free charge fluctuation such as in conductors the wavevector wouldnt be real anymore (more precisely there is attenuation to the field) and magnetic and electric fields wouldnt be in phase.

Actually the response of material depends on the incoming field frequency, the determining quantity is σ/(εω) where σ, ε, and ω are conductivity, permittivity, and frequency respectively. The bigger that quantity the closer the material to behave as a conductor. For example water can behave as a conductor within certain frequency region.
 
  • #5
sophiecentaur
Science Advisor
Gold Member
24,275
4,306
Why are electric and magnetic fields in an electromagnetic wave in phase? Can somebody please explain that???
For a wave in free space, they are in phase, You can justify that by looking at the solution to the wave equation, starting with Maxwells equations. See this link.
 

Related Threads for: EM waves

  • Last Post
2
Replies
30
Views
3K
Replies
7
Views
743
Replies
18
Views
33K
Replies
1
Views
3K
Replies
2
Views
2K
Replies
4
Views
525
  • Last Post
Replies
2
Views
498
Top