What is Electromagnetic field: Definition and 233 Discussions
An electromagnetic field (also EM field) is a classical (i.e. non-quantum) field produced by accelerating electric charges. It is the field described by classical electrodynamics and is the classical counterpart to the quantized electromagnetic field tensor in quantum electrodynamics. The electromagnetic field propagates at the speed of light (in fact, this field can be identified as light) and interacts with charges and currents. Its quantum counterpart is one of the four fundamental forces of nature (the others are gravitation, weak interaction and strong interaction.)
The field can be viewed as the combination of an electric field and a magnetic field. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field. The way in which charges and currents interact with the electromagnetic field is described by Maxwell's equations and the Lorentz force law. The force created by the electric field is much stronger than the force created by the magnetic field.From a classical perspective in the history of electromagnetism, the electromagnetic field can be regarded as a smooth, continuous field, propagated in a wavelike manner. By contrast, from the perspective of quantum field theory, this field is seen as quantized; meaning that the free quantum field (i.e. non-interacting field) can be expressed as the Fourier sum of creation and annihilation operators in energy-momentum space while the effects of the interacting quantum field may be analyzed in perturbation theory via the S-matrix with the aid of a whole host of mathematical technologies such as the Dyson series, Wick's theorem, correlation functions, time-evolution operators, Feynman diagrams etc. Note that the quantized field is still spatially continuous; its energy states however are discrete (the field's energy states must not be confused with its energy values, which are continuous; the quantum field's creation operators create multiple discrete states of energy called photons.)
Hello, I'm new to this forum. I have a short question that I can't solve on my own, I've consulted many books but I can't find solutions, I hope you can help me.
Then considering a conductor traversed by an electric current that varies over time, it produces an electromagnetic field, under...
I was just thinking that if we keep the wire in, suppose, XZ plane and the magnetized needle also in XZ plane. Then in which direction will the needle point? we're going to have either +j cap or -j cap direction by drawing out the tangent at the point where the needle is kept. But a needle could...
I've been trying really hard to calculate the forces between a permanent magnet that is within an electromagnetic field.
I have tried every formula under the sun, but it seems I am just not using the right ones, as my results always end up nonsensical.
To be clear, I am trying to understand the...
INTRODUCTION
From the boundary conditions of the electromagnetic field in perfect conductors, it is deduced that in a transmission line with a time-varying current, the field vectors E and B in the dielectric lie in planes transverse to the conductors and also that the E field is normal to the...
How does an electric field of a moving charge, for example a moving electron, inside a wire looks like? Does it looks like this with distorted circular radial lines?
Obviously at point charges, but where along boundaries? Would they theoretically occur in superconductors since they can carry infinite current (J -> infinity)?
My Progress:
I tried to perform the coordinate transformation by considering a general function ##f(\mathbf{k},\omega,\mathbf{R},T)## and see how its derivatives with respect all variable ##(\mathbf{k},\omega,\mathbf{R},T)## change:
$$
\frac{\partial}{\partial\omega} f =...
hello,
1. according to Robert Wald, General Relativity, equation (4.2.22)
the magnetic field as measured by an observer with 4-velocity ## v^b ## is given by
## B_a = - \frac {1}{2} {ϵ_{ab}}^{cd} F_{cd} v^b ##
where ## {ϵ_{ab}}^{cd}##, the author says, is the totally antisymmetric tensor (for...
Before introducing Special Relativity, a textbook highlights the inconsistency of Maxwell's Electrodynamics and Newtonian Mechanics through the standard discussion about the velocity of light in different frames of reference.
A further inconsistency discussed.
In some inertial frame of...
Hi everyone,
It is about the quantization of the electromagnetic field. The expression of field E and B are defined with:
-the annihilation a- and creation a+ operators, and the frequency ω.
So my question is: how does these fields must be expressed if they where "static"? I mean, how the...
Hai guys,
My background is from tissue engineering more towards to biology. I am doing exposure of electromagnetic field to a human sample.
I have been assigned to use the magnetic device with the information as followed:
The PIC16F886 generates 150 microseconds (µs) of pulse frequency of 80...
What is the relationship between the electromagnetic field and space-time? I am basically assuming that space-time is one big gravitational field.
Is there a relationship between space-time and the field (I presume) created by the strong force (however negligible it may be at any significant...
I'm not sure where this belongs, I'm guessing biomedical, but I'm interested from a physics perspective.
Do neurons generate an electromagnetic field? In other words, all the neural activity in the brain, does it generate electromagnetic fields?
If so, what are the details of these fields?
I...
It is the first time that I am faced with a complex field, I would not want to be wrong about how to solve this type of problem.
Usually to solve the equations of motion I apply the Euler Lagrange equations.
$$\partial_\mu\frac{\partial L}{\partial \phi/_\mu}-\frac{\partial L}{\partial \phi}=0$$...
Allow me to hijack this thread for a second: a photon is an excitation of the electromagnetic field, right? The photon does not exist until measured. So how can we send a photon in a particular direction, so it has a known position and momentum?
I've already made a post about this topic here, but I realized that I didn't understand the explanation on that post. in Chapter 7 of Rindler's book on relativity, in section about electromagnetic field tensor, he states that
_and introducing a factor 1/c for later convenience, we can ‘guess’...
We relating to an electromagnetic radiation as waves.
and in waves there is maximum point and minimum point but when there is permanent electromagnetic level there is no disorder or weave . so is it possible to measure it in blank space relative to other places
My guess is that the force per volume is:
$$ \vec F_V = \rho \alpha x \hat x + \vec J \times \beta x \hat y$$
but I'm not sure where to go after that. I'm not given a value for either the charge density or the current density, so I can't simplify the relation much. Further, I'm not sure if my...
Hello,
I am still trying to fully grasp the general idea of the EM field, which always travels at the speed of light regardless of the reference frame, and is represented by a tensor with 16 components in relativity theory. My understanding is that, depending on the observer's frame of...
I am trying to answer exercise 5 but I am not sure I understand what the hint is implying, differentiate with respect to ##p_\alpha## and ##p_\beta##, I have done this but nothing is clicking. Also, what is the relevance of the hint "the constraint ##p^\alpha p_\alpha = m^2c^2## can be ignored...
I am interested in showing a visualization of water molecules in a time-varying electric/magnetic field as part of my PhD work.
I would like something like this visualization:
, but with an external time-varying field applied.
At first, I thought of simply animating water molecules...
In David Tong's QFT notes (see http://www.damtp.cam.ac.uk/user/tong/qft/qft.pdf , page 131, Eq. 6.38) the expression for canonical momentum ##\pi^0## is given by ##\pi^0=-\partial_\rho A^\rho## while my calculation gives ##\pi^\rho=-\partial_0 A^\rho## so that ##\pi^0=-\partial_0 A^0##. Is it...
Summary: Does a static magnetic field affect a weaker pulsed magnetic field close by?
If you have a static magnet close to a low level pulsed electromagnetic field, will the static magnetic field influence the pulsed field if the static magnetic field is the same strength or stronger than the...
I am searching information about the interplanetary magnetic field,e.g, what is its strength? Does it vary with time? (I guess so) Are there statistical model to predict its variation in space and time? ...
At the moment I have not a specific question in my mind, but I am looking for some...
Homework Statement
I am trying to reproduce MTW's ADM version of the field Lagrangian for a source free electromagnetic field:
##4π\mathcal {L} = -\mathcal {E}^i∂A_i/∂t - ∅\mathcal {E}^i{}_{,i} - \frac{1}{2}Nγ^{-\frac{1}{2}}g_{ij}(\mathcal {E}^i\mathcal {E}^i + \mathcal {B}^i\mathcal {B}^i) +...
The energy density of an electromagnetic field with a linear dielectric is often expressed as . It is also known that energy can be found by . Using the latter, the energy density is found to be , as is well known. If you integrate the latter only over free charge and ignore bound charge, you...
Is there a difference between the meaning of charge conjugation in Relativistic Quantum Mechanics and its meaning in Quantum Field Theory?
In chapter 4.7.5 of "Thomson Modern Particle Physics" the charge conjugation operator is derived without changing the electromagnetic field Aμ. This...
Homework Statement
We have an incident electric field, and there are two cases:
1) the field is polasised perpendicularly to the incidence plane (TE)
2) polarised in the plane (TM)
Here I must be able to correctly apply the limit conditions, to find the Fresnel formulas that give the...
When there is electric charge, then there is an electric field in space aorund it. Or when the electric charge is moving (without acceleration), then it is produced magnetic field in a space around it. Both of these fields permeated to infinity according to Maxwell theory. But how fast...
Homework Statement
A laser tweezer is a laboratory instrument, which uses highly focused laser beams to ‘trap’, hold or move small sized objects. The principle of the operation is that in the focal spot, the light intensity is inhomogeneous, and acts on the particle with a force that points...
As I understand space time fabric is exclusively the Gravitational field according to Einstein.So every field wave or interaction is contained in the Gravitational Field.This fabric of spacetime(gravitational field) is having properties of inertia and elasticity that is why gravitational waves...
Homework Statement
Consider an electromagnetic field in an empty space in the region ##0 \leq z \leq a## with the following non-zero components:
$$E_x = -B_0\frac{\omega a}{\pi}\sin\left(\frac{\pi z}{a}\right)\sin\left( ky-\omega t\right)\\
B_z = B_0\frac{ka}{\pi}\sin\left(\frac{\pi...
So I'm kind of confused. The way I understand it, an electromagnetic field is just a regular electric field viewed from a relativistic point of view, meaning that since we see the charges moving relative to us, we feel like the particles and the fields created by them come closer together (I...
Susan Pocket claims that part of the electromagnetic field of the brain is consciousness and that conscious qualities such as a red car are spatially patterned electromagnetic fields. She also claims that the quantum spatial scale is irrelevant. Intuitively it seems to me Quantum electrodynamics...
Why does my laptop's screen refresh every time I bring a metal object (any size) to my electric lighter?
-Happens when I am 1 foot away from the laptop
-1 foot away from the external monitor's wires (HDMI & power)
1. Video footage (MUST WATCH)
NOTE: the laptop screen also flickers a bit
NOTE...
Homework Statement
[/B]In this question, it asks for the magnetic field associated with the electromagnetic wave.
Homework EquationsThe Attempt at a Solution
The magnetic field is perpendicular to Electric field but it can be in either x or z direction...how do I choose the direction.I
Electromagnetism gives the energy density ##\frac{\epsilon_0}{2}E^2+\frac{1}{2\mu_0}B^2##. It does not include frequency ##\nu## or ##\omega## at least explicitly that QM or photon needs. For an example static electric field has nothing to do with frequency but has energy. How should I...
Homework Statement
A metal rod can slide on a rail without any friction in the presence of uniform magnetic field of B=1T which is perpendicular to the plane of the paper.The distance between the tracks is d=0.1m and the resistance given is R=0.1 ohm.The resistance of the rail is negligible and...
I have a question connected with the problem:
https://www.physicsforums.com/threads/continuity-equation-in-an-electromagnetic-field.673312/
Why don’t we assume H=H*? Isn’t hamiltonian in magnetic field a self-adjoint operator? Why? Why do we use (+iħ∇-e/c A)2 instead of (-iħ∇-e/c A)2 two times?
Gravity bends light because all charged particles have mass and all electric field starts and ends on some charge particle. Is that a viable explanation for this phenomenon?
As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other.
Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to...
Homework Statement
This is problem (7.1) from John A. Peacock "Cosmological Physics".
Show that the first-order perturbation term for quantum mechanics with an electromagnetic field, ##(e/m) \mathbf{A \cdot p}## is proportional to the electric dipole moment. What is the interpretation of the...
Hi. This might be really basic. But I am really struggling to grasp the difference between electrical currents such as AC and DC and RF. For the case of AC current, it alternates currents at a certain frequency.. which makes me wonder how AC and RF are different.
Also, if you could, could you...
Hi everyone!
I've been reading about these topics (Feynman lectures and more on the internet and some books) but I still have a doubt, maybe because I haven't understood the whole of it.
This is my doubt: Think of an imaginary situation in which we have an accelerating charge. The...
As far as I know, we can describe the universe as if every bodies uses to follow a straight path in a curved space-time. What kind of role does the electromagnetic field play in all of this? Can we associate a "space-like" field curved by the charge of the particle with it?
Does the...
As I understand it, the classical source-free electric, ##\mathbf{E}## and magnetic, ##\mathbf{B}## wave equations are solved by solutions for the electric and magnetic fields of the following form: $$\mathbf{E}=\mathbf{E}_{0}e^{i (\mathbf{k}\cdot\mathbf{x}-\omega t)}$$...
As the title suggests, I'm looking for a way to explain/describe the EM field to high school seniors. Mechanical transverse waves are easy. But since EM waves travel in a vacuum and require no medium it's hard to form a picture in the mind of the students. What is actually moving?