# 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.)

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1. ### I EM field and EM wave

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...
2. ### Magnetic field pointing into a normal magnetized compass needle

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...
3. ### I Permanent Magnetic Dipole in an electromagnetic field

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...
4. ### A Voltage and current waves in a transmission line

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...
5. ### B Exploring the Electric Field of a Moving Charge

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?
6. ### I Where do discontinuities in the electromagnetic field occur?

Obviously at point charges, but where along boundaries? Would they theoretically occur in superconductors since they can carry infinite current (J -> infinity)?

26. ### A Interplanetary electromagnetic field

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...
27. ### ADM field Lagrangian for a source-free electromagnetic field

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) +...
28. ### Energy density of an electromagnetic field

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...
29. ### A Does Charge Conjugation change the electromagnetic field?

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...
30. ### Finding Fresnel coefficients from the interface conditions

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...
31. ### Electromagnetic Field vs Electromagnetic Wave

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...
32. ### How does a dielectric interact with a laser beam?

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...
33. ### Electromagnetic wave, electromagnetic field and quantas

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...

50. ### Looking for a way to describe Electromagnetic Field

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?