Electromagnetic field Definition and 235 Threads

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. F

    Physical degrees of freedom of an Electromagnetic field

    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: $$\mathbf{E}=\mathbf{E}_{0}e^{i (\mathbf{k}\cdot\mathbf{x}-\omega t)}$$...
  2. G

    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?
  3. physea

    Is energy needed to maintain an electromagnetic field?

    Hello Is we apply a voltage at the ends of a coil, a magnetic field will be generated? Is that correct? Will that empty the battery that is responsible for the voltage or a partial energy from the battery will be stored in the magnetic field of the coil and after that the battery will not...
  4. Arman777

    Electromagnetic Field in Empty Space

    Our Professor said there will be still an electric field in empty space even without charges.Hows that possible.Space-time has a some quantum property that acts like this ?
  5. S

    Particle in an Electromagnetic Field

    Using the Lagrangian : L = ½mv^2 - qφ + qAv What is the physical intuition of Av ? I know that A is the magnetic vector potential and that v is the velocity of the charged particle. I just don't know what their dot product means physically .
  6. T

    I Lagrangian for electromagnetic field derivation

    " We can put the Lorentz force law into this form by being clever. First, we write $$\frac{dA_j}{dt}=\frac{d}{dt}(\frac{\partial{}}{\partial{v_j}}(v.A)),$$ since the partial derivative will pick out only the jth component of the dot product. Now, since the scalar potential is independent of the...
  7. M

    How Can Dynamic EMF Variation Enhance Bone Fracture Healing in Animal Studies?

    I am developing a setup to generate dnamic eletromagnetic fields (EMF) which will be used to study the effect of EMF on bone francture healing in small animals.The setup has two solenoid coils which are separated by a distance and connected in series. Both coils are excited by 15 V AC that...
  8. Mihai_B

    I Solve Electromagnetic Field Acting on Charged Particle

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  9. Narayanan KR

    Can capacitors receive EM energy?

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  10. T

    How Can Electromagnetic Waves Translate into Audio Frequencies?

    Hi! For project in one of my classes, I have to research a super power and a possible scientific explanation of it, showing either why it can or can't happen. I chose a super power of translating people's electro magnetic fields into frequencies, and being able to translate that into...
  11. M

    A Quantized E field, Coulomb Gauge with Interactions

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  12. G

    Canonical momentum of electromagnetic field

    The momentum canonical to the electromagnetic vector field A is straightforward to compute, as is explained in textbooks or webfiles (for example Bjorken-Drell or http://www.physics.buffalo.edu/gonsalves/aqm/lectures/10/lec-10.pdf ). Its time component is zero, while the spatial components are...
  13. Muratani

    I Relation between Poincare matrix and electromagnetic field t

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  14. T

    Planes waves produced from a current sheet

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  15. P

    Ampere's Law: Explained and the Role of Magnetic and Electric Fields

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  16. C

    Which Sensor Setup Wins the Race: 80ft Wide Field or 20ft Wide Spaceship?

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  17. S

    Energy-Momentum Tensor for the electromagnetic field

    Homework Statement Maxwell's Lagrangian for the electromagnetic field is ##\mathcal{L}=-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}## where ##F_{\mu\nu}=\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}## and ##A_{\mu}## is the ##4##-vector potential. Show that ##\mathcal{L}## is invariant under gauge...
  18. Konte

    I Quantization of electromagnetic field

    Hello everybody, It is known that electric field operator is shown as \hat{E}(r,t)=-i\sum_{k,\lambda}\sqrt{\frac{\hbar\omega_k}{2\epsilon V}}\left(a(t)^\dagger_{k,\lambda} e^{-ik.r} - a(t)_{k,\lambda} e^{ik.r} \right) \hat{e}_{k,\lambda} But if I need to represent an electrostatic field in a...
  19. T

    Why is the electromagnetic field not a 'charge field'

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  20. pioneerboy

    EM length of gravitational waves

    Maybe a stupid question and maybe sensless to ask, but as I don't know, I ask anyway: what is the length of the newly found gravitational waves in terms of traditional EM wavelengths?
  21. S

    How to Determine Electric Fields and Charge Distributions Between Metal Slabs?

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  22. J

    Quantum fluctuations within an electromagnetic field

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  23. M

    Measuring low Electromagnetic field

    Hi, I am working on a project where I've to make an electromagnet and very very low amount of current (micro amp to nano amp) will be supplied to the electromagnet. And finally have to measure the magnetic filed with a sensor. My question, is it feasible to generate measurable magnetic field...
  24. S

    Differences between solenoidal and rotational vector fields?

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  25. F

    Can anyone explain this anomaly?

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  26. TardisRobber

    Harnessing Electricity from an Electromagnetic field?

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  27. G

    How Fourier components of vector potential becomes operators

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  28. darida

    Components of The Electromagnetic Field Strength Tensor

    Source: http://gmammado.mysite.syr.edu/notes/RN_Metric.pdf Section 2 Page: 2 Eq. (15) The radial component of the magnetic field is given by B_r = g_{11} ε^{01μν} F_{μν} Where does this equation come from? Section 4 Page 3 Similar to the electric charges, the Gauss's flux theorem for the...
  29. E

    What is the intensity of an electromagnetic radiation?

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  30. P

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  31. T

    Pulsed electromagnetic field indicator

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  32. M

    Help with radio waves and electromagnetic fields

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  33. J

    Classical Book like Barret/Bekefi's Electromagnetic Vibrations?

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  34. USeptim

    Electromagnetic field 4-momentum density and inertial frames

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  35. Dvorak

    Magnetic field created without an electromagnetic field?

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  36. mgkii

    Energy at zero axis in an Electromagnetic field?

    Can someone correct my understanding on electromagnetic waves please; I've clearly got the wrong end of a stick somewhere, but can't figure out where my misunderstanding is! Thanks. If I draw a classic EM wave with the electric field on the up and down axis and the magnetic field at right...
  37. Strangelet

    Problem with Maxwell Lagrangian Density

    Homework Statement I have to expand the following term: $$\dfrac{1}{4} F_{\mu\nu}F^{\mu\nu} = \dfrac{1}{4} \left(\partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}\right) \left(\partial^{\mu}A^{\nu} - \partial^{\nu}A^{\mu}\right)$$ to get in the end this form...
  38. S

    Could this experiment prove special relativity to be wrong?

    Think about an electric charged object moves linely, it will produce current hence the magnetic field. But if the obserser moves together with the electron charged object, so there is no relative movement between them, that means the electric charged object is static to the observer, hence...
  39. F

    Electromagnetic field on molecule

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  40. A

    Hamiltonian for a free electron in electromagnetic field

    hello, how to derive the hamiltonian for a free electron in electromagnetic field mathematically ? for a first step what is the lagrangian for a free electron in the EM field in classical mechanics ? the physics textbook always like to give the results directly.
  41. V

    How to Show the Vanishing of a Term in Electromagnetic Field Energy Calculation?

    Hey everyone! I am supposed to calculate the energy contribution of the magnetic field term of an electromagnetic field. Basically the term is the following: \int_\Omega dx^3 (curl(\vec{A}))^2 And we can use the following two equations for simplifying: div(A)=0 and \Box A=0 So basically...
  42. R

    MRI Electromagnet Interference in a Figure-8 cable

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  43. R

    Deriving the electromagnetic field strength tensor

    Just one last question today if someone can help. I'm trying to derive the electromagnetic field strength tensor and having a little trouble with (i think) the use of identities, please see below: I understand the first part to get -Ei, but it's the second line of the next bit I don't...
  44. W

    How big does a magnet need to be to move X amount of KGs

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  45. Z

    Elastic Potential Energy to Aid Electromagnetic Induction

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  46. B

    Planetary Electromagnetic Field

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  47. S

    Total Magnetic Flux Density Law Problem

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  48. P

    Shape of electromagnetic field

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  49. J

    Calculation and application of dyadic Green's function

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  50. W

    Quantization of EM field in dielectric?

    hi , what is the equation for the hamiltonian of EM field in dielectric and how can we say we have quantized the hamiltonian?
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