- #1
vebrown
- 24
- 0
What is the phase relationship between the magnetic component and the electric component of an electromagnetic field. Is it in phase, or 90 degrees out of phase. I see it both ways in a Google search ?
quasar987 said:The electric and magnetic field oscillate in phase (i.e. when E is at its maximum, so is B, etc.), but their direction of oscillation is perpendicular.
Claude Bile said:Further to rbj's post I would also like to point out that waves in media (including hollow waveguides) and resonators also do not have their E and B fields in phase.
quasar987 said:Really Claude, you're worrying me. Did I read you right when you said that in matter, E and B (D and H) are not in phase?
This is not correct, the fields are in-phase. This is a fairly common question, here is my explanation a couple of days ago.Psyrick said:Electric and magnetic field vectors are 90 degrees out of phase in electromagnetic wave propagation. ... The magnitude of one vector results from the differential of the other, meaning one will be changing fastest as it aproaches zero magnitude, while the other aproaches maximum or minimum, hence, 90 degrees out of phase.
DaleSpam said:Wannabeagenius is correct. They are in-phase, not 90 degrees out of phase.
If you look at Maxwell's laws in vacuum you will find that it is not quite corect that "a changing magnetic field induces an electric field". It is more correct to say "a changing magnetic field induces curl of an electric field" or in other words "a changing magnetic field (in time) induces a spatially changing electric field". When you express it correctly you immediately see that the electric and magnetic fields should be in phase.
If you look at Maxwell's laws in vacuum you will find that it is not quite corect that "a changing magnetic field induces an electric field"
No, it doesn't. See my explanation above.Psyrick said:If you look at Faraday's law of induction, you will find it supports my argument.
The term emf stsnds for electromotive force, which is a voltage or electric potential difference capable of creating an electric current. From quantitative experiments, Faraday determined that emf induced in a coil of N loops depends on the time rate of change of the number of magnetic field lines through all the loops, or the time rate of change of the total magnetic flux. This dependance, known as Faraday's law of induction, is expressed mathematically as:
EMF = - N (ΔФ / Δt)
Where ΔФ = Change in magnetic flux through one loop
Δt = Change in time
N = Number of turns in the loop
(Wilson, Buffa, and Lou 657-659)
The EMF generated is proportional to the rate of change of the magnetic flux. (Ulaby 255)
Tell me Psyrick, for a EM plane wave propagating in free space what is the number of turns in the loop, N? This expression is obviously not the general one (it is for EMF in a loop of circuit), and it is not applicable for a wave propagating in free space.Psyrick said:Indeed, I can.
This dependance, known as Faraday's law of induction, is expressed mathematically as:
EMF = - N (ΔФ / Δt)
Where ΔФ = Change in magnetic flux through one loop
Δt = Change in time
N = Number of turns in the loop
The energy goes in the direction of the Poynting vector. Remember, the fields are varying in space and time, not just time.Psyrick said:If both fields fluctuate in matched phase, where then does the energy stored within the fields go to and come from as the field magnitudes change?
a time-varying B field induces a spatially varying E field. For a sinusoidal plane wave the spatial variation is highest at the zero crossing and the time variation is also highest at the zero crossing. Therefore, they are in phase.
Sure. Let's say that we are working with a monochromatic plane wave propagating in the z direction, and let's say that the phase between the E and B field is unknown and see if we can solve for it.Psyrick said:Can you describe the phase relationship considering time as a variable of constant rate?
The phase relationship in an electromagnetic wave refers to the relative timing or position of the peaks and troughs of the wave. It describes the relationship between the electric and magnetic fields of the wave as they oscillate in time and space.
Phase relationship is measured in degrees or radians, and is often represented on a graph as a phase angle. The phase angle represents the fraction of a full cycle that has been completed at a given point in time.
The phase relationship in electromagnetic waves is important because it affects the behavior and properties of the wave. It determines factors such as interference, polarization, and diffraction.
The phase relationship can vary depending on the type of electromagnetic wave. For example, in a plane wave, the electric and magnetic fields are in phase with each other, while in a circularly polarized wave, they have a constant phase difference of 90 degrees.
Yes, the phase relationship of an electromagnetic wave can be manipulated through various techniques such as phase shifting, modulation, and interference. These techniques are used in many applications, including communication systems and signal processing.