Electromagnetism Definition and 853 Threads

Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation. At high energy, the weak force and electromagnetic force are unified as a single electroweak force.

Electromagnetic phenomena are defined in terms of the electromagnetic force, sometimes called the Lorentz force, which includes both electricity and magnetism as different manifestations of the same phenomenon. The electromagnetic force plays a major role in determining the internal properties of most objects encountered in daily life. The electromagnetic attraction between atomic nuclei and their orbital electrons holds atoms together. Electromagnetic forces are responsible for the chemical bonds between atoms which create molecules, and intermolecular forces. The electromagnetic force governs all chemical processes, which arise from interactions between the electrons of neighboring atoms. Electromagnetism is very widely used in modern technology, and electromagnetic theory is the basis of electric power engineering and electronics including digital technology.
There are numerous mathematical descriptions of the electromagnetic field. Most prominently, Maxwell's equations describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
The theoretical implications of electromagnetism, particularly the establishment of the speed of light based on properties of the "medium" of propagation (permeability and permittivity), led to the development of special relativity by Albert Einstein in 1905.

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  1. L

    Work to bring a charge to the center of two quarter circles

    By measuring angle \theta from the positive ##x## axis counterclockwise as usual, I get ##d\vec{E}=k( (\lambda_2-\lambda_1)\cos(\theta)d\theta, (\lambda_2-\lambda_1)\sin(\theta)d\theta )## and by integrating from ##\theta=0## to ##\theta=\frac{\pi}{2}## I get...
  2. L

    An iron cylinder inside a solenoid

    From ##\oint_{\Gamma}\vec{H}\cdot d\vec{l}=\sum I## by Ampere's Law which gives ##H \Delta l=\Delta N\cdot i\Leftrightarrow H=n i## where ##n=## number of turns per unit length so ##i=\frac{H}{n}=\frac{10^3 A / m}{\frac{200}{0.2m}}=1 A##. Since ##\vec{H}=\frac{\vec{B}-\mu_0\vec{M}}{\mu_0}## we...
  3. L

    A disconnected capacitor with two dielectrics in parallel

    I considered the capacitor as two capacitors in parallel, so the total capacitance is ##C=C_1+C_2=\frac{\varepsilon_0\varepsilon_1 (A/2)}{d}+\frac{\varepsilon_0\varepsilon_2 (A/2)}{d}=\frac{\varepsilon_0 A}{2d}(\varepsilon_1+\varepsilon_2).## Since the parallel component of the electric field...
  4. iochoa2016

    I Measuring characteristic impedance as suggested by KRAUS' book

    Can someone provide more information about this method to measure chracteristic impedance using resistance paper?. Kraus' book claims that the characteristic impedance can be measured by simple dc measurement. It even shows a case to mesure the impedance of a coaxial cable with square outer...
  5. L

    Magnetization of ferromagnetic material

    I have thought about the following ##\oint \vec{H}\cdot d\vec{l}=0\Leftrightarrow H_{int}(D-h)+H_{ext}h=0\Leftrightarrow (\frac{B}{\mu_0}-M)(D-h)+\frac{B}{\mu_0}h=0\Leftrightarrow M=\frac{D}{D-h}\frac{B}{\mu_0}## but (supposing what I have done is correct) I don't understand which value of ##B##...
  6. L

    Magnetic Surface Currents and the Interaction of Magnetic Fields with Matter

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  7. L

    Doubts on Exercise Wording: Energy Density & Poynting Vector

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  8. L

    Potential due to a finite charged wire

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  9. L

    Maximum charge on a spherical capacitor

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  10. warhammer

    I Guidance Requested on Inductance Formula for Solenoid

    In my textbook on EM, the formula for self inductance of a finite solenoid is given as: L= (μ(o)* N^2*A * {√(a^2+ l^2) - a} )/l^2 where a=Radius of each turn, l=length of solenoid. I am having trouble and extreme difficulty in trying to ascertain how this formula was derived in the book and...
  11. A

    Trajectory of an electron traveling near a current-carrying wire

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  12. F

    I EM Power transmitted from one region to another (normal incidence)

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  13. Z

    Understanding the electric force felt by the charges on a sphere

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  14. Z

    How to interpret a passage in Purcell's Electricity and Magnetism

  15. Dario56

    I Energy Flow From Battery to the Light Bulb

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  16. Z

    On which objects can we apply Gauss' Law to find the electric field?

    What am I missing? I also don't get the title of the section: "Charge distributions with enough symmetry for Gauss's Law". I thought Gauss's Law was valid for any closed surface enclosing a charge. I don't understand what "enough symmetry" means in the title above. I get that with symmetry...
  17. Z

    Electric field is constant around charged infinite plane. Why?

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  18. godiswatching_

    What is the effect of a 1 cm gap on the magnetic field in a solenoid?

    Hey, I was trying to figure out this problem. I got (a) using B = mu * NI/L but I'm not sure how to start the part about the magnetic field in the gap after the solenoid is ripped in half with 1 cm gap. Thanks for the help!
  19. Z

    Calculate the electric field due to a charged disk (how to do the integration?)

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  20. Z

    Electric field created by two charged circular arcs?

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  21. Z

    How to choose the correct function to use for a Taylor expansion?

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  22. Z

    MIT OCW 8.02 Electromagnetism: how were these two limits calculated?

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  23. Andreea007

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  24. K

    I Gauge in the Aharonov Bohm effect

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  25. A

    I Electron two-slit experiment in classical electromagnetism

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  26. Falgun

    Classical Can Purcell and Griffiths Be Studied Together for Electromagnetism?

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  27. S

    I How are the Maxwell's Electromagnetism equations traceless?

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  28. P

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  29. M

    I A problem when trying to compare electromagnetism with gravity

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  30. sergiokapone

    I Can Electromagnetic Fields Exist Independently of Charges?

    Interesting thing, the undergraduate courses of electromagnetism states the electromagnetic field caused by electric charge: d∗F=4π/c∗J, and students, in my opinion, mistakenly imagine the electromagnetic field as a product of charged particle. In my opinion, it is more correct to say that...
  31. Viona

    B The resistance of an ohmic conductor

    I know that the resistance of an ohmic conductor increases with length because the electrons going through the conductor must undergo more collisions in a longer conductor. But why decreasing the cross-sectional area of the conductor also increases the resistance of a conductor?
  32. E

    Electromagnetism and the movement of particles

  33. MarcelloP

    Is it Possible to Create a Large but Low-Powered Electromagnet?

    Hi to everyone! I'm currently working on a University project and one of my crazy ideas needs me to get my hands on a pretty strange electromagnet. the measurements are 40cm by 40cm with a height of 3 to 5 cm (doesnt matter a lot) i don't need this magnet to be very powerful (just enough to...
  34. D

    Can any object cause fluctuations in a magnetic field?

    Summary:: Can a moving object cause disruptions in a magnetic field that could be detectable? Hello, I was hoping someone could assist me on a query I have regarding disruptions in a magnetic field. For some context, I am creating a science fiction story which features a non-humanoid alien...
  35. Ale_Rodo

    Lorentz force acting upon an electron moving in a circle

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  36. sophiatev

    Electrostatic Potential Energy of a Sphere/Shell of Charge

    So it seems the typical way to approach this problem is to consider the sphere when it has charge q and radius r. With uniform charge density ##\rho##, this becomes ##q = 4/3 \pi r^3 \rho## and so ##dq = 4 \pi r^2 dr \rho##. Using our expression for the potential outside of the sphere, we find...
  37. U

    Clarification on electric quadrupole moment definition

    I have encountered two (?) definitions of the electric quadrupole moment. They are: $$Q_{ij}=\frac{1}{2}\int \rho(\vec{x}')x'_i x'_j\,\mathrm{d}^3x'$$ and $$Q_{ij}=\int (3x'_i x'_j-\delta_{ij}x'^2)\rho(\vec{x}')\,\mathrm{d}^3x'$$ I am trying to study radiation arising from the electric...
  38. Marshall2389

    B How does a photon not "feel" electromagnetism?

    I've attached a picture of a table in Sean Carroll's The Particle at the End of the Universe. It says that photons don't "feel" electromagnetism, but gluons feel the strong force, the W and Z bosons feel the weak force, and gravitons feel gravitation. How is this so? (I have no formal quantum...
  39. J

    Electromagnetic inertial reaction force?

    I accelerate charged particle ##A## causing virtual photons to travel to distant charged particle ##B## which feels an electromagnetic force proportional to ##A##'s acceleration (for a classical field description of this effect see https://www.feynmanlectures.caltech.edu/I_28.html Eqn 28.6)...
  40. A

    Electromagnetism - movement of a coil in a magnetic field

    So my idea was that to reach the equilibrium position, the final moment of force has to be 0 (so in the end the forces will “eliminate” each other). And I found the equation Fm=B*I*l*sinα, which should characterize the force, which affects wire with the current in a magnetic field, and Fleming’s...
  41. LCSphysicist

    I General relativity, Electromagnetism and Feynman Diagrams

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  42. K

    Classical Best undergraduate electromagnetics textbook

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  43. Karimselim1997

    A Is There a Unified Theory Between General Relativity and Electromagnetism?

    I want know is there any unified and consistent theory between general relativity and electromagnetism ? If yes could you provide me any textbook ? I'm interest
  44. Pouramat

    Energy-Momentum Tensor for Electromagnetism in curved space

    a) I'd separated the Lagrangian into: $$ \mathcal L = \mathcal L_{Max}+\mathcal L_{int} $$ in which ##\mathcal L_{Max} =\frac{-1}{4}\sqrt{-g} F^{\mu \nu}F_{\mu \nu}## and ##\mathcal L_{int} =\sqrt{-g} A_\mu J^\mu## Thus: $$ T^{\mu \nu}_{Max}= F^{\mu...
  45. C

    Electromagnetism and the Pauli Exclusion Principle

    Electromagnetism in the atoms is why we can't pass through a bank vault. But supposed electromagnetism were canceled for an object, what would happen to the residual or remaining Pauli Exclusion principle? Would it still cause resistance to passing through the vault? On a second scenerio, what...
  46. J

    I Does Poynting's Theorem only involve external fields?

    Poynting's Theorem (https://en.wikipedia.org/wiki/Poynting's_theorem) says: The rate of energy transfer (per unit volume) from a region of space equals the rate of work done on a charge distribution plus the energy flux leaving that region. $$-\frac{\partial u}{\partial...
  47. hagopbul

    Question about this Continuity Equation (electromagnetism)

    Hello All : reading the Bo Thide book in electromagnetism , downloaded the draft copy from the following link http://www.plasma.uu.se/ , i reached the chapter 4 now and a section in that chapter (section 4.3) have few lines that i coudnt understand (mathematically speaking) the writer conclude...
  48. U

    Derivation of torque on general current distribution

    How do I simplify the expression...
  49. Arman777

    Classical Relativistic Electromagnetism (Undergrad Level)

    I have looked several special relativity books but in each of them the metric is defined as ##\eta_{\nu\mu} = (+1, -1, -1, -1)##. Is there a book where the metric is defined as ##\eta_{\nu\mu} = (-1, +1, +1, +1)## ?
  50. TechieDork

    Find an expression for a magnetic field from a given electric field

    Here this is my attempt : Reference Textbook : Zangwill's Modern Electrodynamics I stuck at the last step , I really have no idea what to do next.
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