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. S

    How Does Electromagnetism Affect a Charged Particle at a Point?

    Homework Statement The magnitude of the magnetic field in teslas at a distance d from a long straight wire carrying a current I is given by the relation B = 2 X 10 7 I/d. The two long straight wires shown above are perpendicular, insulated from each other, and small enough so that they...
  2. F

    Electromagnetism, Relativity, Force, Space ?

    Hey there! I was just listening to Richard Feynman on the way home and hit yet another issue I have with relativity... I'd be most thankful for any input! :) So, suppose we got two charged particles moving parallel to each other. A charged particle has an electrical field - if it's moving...
  3. G

    Electromagnetism Homework: How to Solve These Problems?

    Hey everyone, I just wanted to double check some solutions and inquire about a problem. Homework Statement A toroid is a coil of wire wrapped around a doughnut-shaped ring (a torus). For a tightly wrapped toroid with N turns, the magnetic field lines of \vec{B} form concentric circles...
  4. D

    Determine n when you know the charge density (Electromagnetism)

    Homework Statement You are informed that the charge density is: $\rho \left( r \right)=k{{r}^{-n}},r<a$, where k is a constant and n is a whole number. Determine n. Homework Equations Besides that, I know that: \[E=\frac{Q}{4\pi {{\varepsilon }_{0}}}\frac{1}{{{r}^{2}}},r<a\] (E is...
  5. B

    How Can I Start Practical Experiments in Electromagnetism?

    Programmer-turned-amateur-physicist here. I'm reading Feynman's lectures, but I'm urged to do some physical experiments. The thing is, I have no idea about the practical side of things. Could someone write me a detailed description of some experiment? Say, the one with the hanging wire and the...
  6. J

    Electromagnetism Current Curcuits

    Four resistors are connected to a battery as shown in the figure. The current in the battery is I, the battery emf is emf, and the resistor values are R1 = R, R2 = 2R, R3 = 4R, and R4 = 3R. Picture: http://www.webassign.net/serpop/p21-32.gif (a) Rank the resistors according to the...
  7. L

    The apparent arbitrariness in Electromagnetism

    In studying the world, physicists found that, in order to completely understand what today we call "Electromagnetism", it was necessary to do three things: find an equation which describes the electric field under all circumstances, find an equation which describes the magnetic field under all...
  8. T

    Teaching my boys practical electromagnetism

    I need help designing some build-from-scratch DC motors. I'm looking to build really robust motors that I can be be sure will demonstrate clearly the principles involved, but that can be modified by my boys and that they can really *play* with and use to run simple toys. I've already shown...
  9. G

    Electromagnetism: Ways to study it.

    Hello to everyone. I'm quite new here and I just wish I have found this site sooner. I am currently enrolled in Physics 2 class (Introductory) and we have just started Electromagnetism. Quite frankly, I am here to ask for some guidance as I am very weak in Physics. The only reason I passed...
  10. N

    How Is Charge q2 Calculated Using Electric Potential and Field Equations?

    Have exam tomorrow. I know I should have studied before and more, but please help. If you know the answer, please take some time to reply. Thanks very much. Homework Statement There are two charges, q1 = +4.5nC, and q2, ?, which are at distances d1 = 2.5cm and d2 = 2.0cm, from a point...
  11. N

    Some electromagnetism questions

    Can anyone please answer, and if possible, explain, this question? Thanks 1. A battery is connected between A and B of a bar made of semi-conductor of type P. The positive electrode was connected in A and the negative in B. What's the current direction? A. from A to B B. in the semiconductor...
  12. R

    Why is the Dirac Delta Function in the Charge Density Solution?

    Homework Statement the electric potential of some configuration of charge is given by the expression: V(r)= (Ae^(-pr))/(r) where A and p are constants. Find the E-field E(r), the charge density rho(r) and total charge Q. The answer for rho is given in book as: epsilon-not * A *...
  13. R

    Electromagnetism, two wires and fields

    Homework Statement Two very long thin wires carrying equal and opposite currents of 103 A are placed parallel to the x-axis at y=0 and z=+-0.5. Calculte the magnetic field B in the x-y plane and determine it's maximum gradient.Homework Equations I'm having serious trouble understanding the...
  14. M

    Solve the Circuit For Electromagnetism Unit

    Homework Statement please visit this site and solve with calculations, Thank you! http://rapidshare.com/files/338079894/Figure_it_out.doc Homework Equations V=IR Rt=1/R1+1/R2+1/R3 The Attempt at a Solution Please solve this circuit Thank You
  15. S

    Electromagnetism, flux density Vs. field size

    With a set coil if you increase the electric flow does the flux density increase And/or the magentic field decrease/ maintain/ increase in size..? Thanks once again, Sem.
  16. L

    Geometric product in electromagnetism

    Hi. I've been learning how to use geometric algebra and I've been stumbling when I apply it to E&M. I am hoping someone here can point out what I am doing wrong. The problem comes when trying to represent the field tensor in terms of the 4-potential. Here is the standard form: F^{\mu\nu}...
  17. M

    Curvature of path made by electron in electromagnetism

    I got this question on an Assigment, and ..man, am having really hard time with it Here is how it start : "A student used the apparatus shown below to measure the radius of the curvature of the path of electrons as they pass through a magnetic field that is perpendicular to their path. This...
  18. fluidistic

    Electromagnetism question, what formula

    I'd like to know what formula to use in order to find the following : Imagine a uniform magnetic field. I am moving with a constant velocity perpendicularly through it. Do I see only an electric field? A magnetic field? Both? Or both of them? What if I move in the sense of the magnetic...
  19. T

    MIT series on Electromagnetism

    This has been helping me throughout my semester in an intermediate level EM course, so I thought I'd post it here: http://www.youtube.com/view_play_list?p=C2CEECFD938FD494"
  20. L

    Electromagnetism- current carrying conductor and permanent magnet

    Hi. I'm doing an experiment and I'm kinda stuck. I know that a current produces a magnetic field. In this experiment there is a current carrying wire (copper) and a permanent magnet suspended above it. Deflection is being measured as the current is varied. I know that both magnetic...
  21. MathematicalPhysicist

    Electromagnetism question (Vector integration).

    Homework Statement Show that the force caused by external electric field on a charge distribution is given by: F=qE(0)+(p\cdot \nabla)E(0)+... (it's enough to show the first two terms), where E(0) is the electric field in the origin which we choose to develop the expression around it. p is...
  22. PrincePhoenix

    DC doesn't cause electromagnetism?

    DC doesn't cause electromagnetism? That is what our teacher says. Can anyone explain why it doesn't? As far I remember I made an electromagnet from a nail by passing current through it from a battery cell about 6 years ago.
  23. A

    Calculating Dust Particle Size in Solar System Orbit - Electromagnetism Help

    urgent electromagnetism help Homework Statement Assume that dust particle in the solar system are spherical, black and have a density of 2000kg/m^3. Use the total luminosity of the sun to calculate the time average poynting vector of the radiation at a distance r from the Sun. Hence...
  24. S

    Electromagnetism - Quadrupole , Octupole

    1.Calculate the electric field of a quadrupole in spherical coordinates. 2.Calculate the electric field of a octupole in spherical coordinates.
  25. MathematicalPhysicist

    2 questions in electromagnetism.

    Homework Statement 1. In a dilectric sphere with radius a and polarization vector P= P0 r (r is the spherical radial vector) where P0>0. find D,E and the polarization charge volume density and area density. 2. A chagrge q is displaced at the centre of a hollow dilectric sphere (with a,b as...
  26. A

    Electromagnetism Help: Calc Electric Field w/ Gauss's Law

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  27. R

    Electromagnetism, find magnitude and direction of the resulting force on wire.

    A long straight horizontal wire carries a current of 70 amperes towards the east. The wire is placed in a uniform magnetic field of intensity 0.15 T towards the north. Find the magnitude and direction of the resulting force on a 25m length of this wire F=ILB sin \theta F =...
  28. S

    Is gravity really just an electromagnetic field on a larger scale?

    Hi, Apologies an advance for any general ignorance (not a physics student - just happen to have an interest and no background!) Is there generally a strong electromagnetic field associated with any mass demonstrating a strong gravitational field? Are there exceptions? I've heard that...
  29. D

    Limit at which Strong Nuclear force = Electromagnetism

    Is there a defined distance at which Electromagnetism starts exerting more force than the strong nuclear force? So far I have Gluons have <20MeV (32.04×10-13J) of energy. Using the uncertainty principle: t=h/(4×pi×E) and distance = t×c Therefore t = (6.6×10^-34)/(4×pi×<32.04×10^-13)...
  30. F

    Electromagnetism: Charge Density of a Shell

    Homework Statement We learned in E&M about the Dirac Delta function and its applications to representing the densities of point charges in space. For example, the charge density of space with a point charge q at the origin is given by q*delta(r). How does this density representation work with...
  31. T

    Electromagnetism( Vector Calculus)

    Homework Statement Any sites you recommend that can really supplement my understanding of Vector Calculus applied to Electromagnetis? Thanks
  32. Y

    Electromagnetism and Magnetic Flux in a Rectangular Circuit: Homework Help

    Homework Statement Two infinite long straight conductors and a rectangular circuit lies in the same plane. The straight conductors is parallel and got the distance 2a from each other. There runs a constant current of I1 and I2 in both of them, and the current is pointed downwards. The...
  33. F

    What are some examples of fields with equal divergences and different curls?

    Find a pair of fields having equal and divergences in some region, having the same values on the boundary of that region, and yet having different curls. I really have no idea on where to start for this. Would making up 2 arbitrary fields in spherical co-ordinates work? a(theta) + b\phi +...
  34. P

    Prerequisites for Electromagnetism?

    Hi, Just out of curiosity, what should I know if I am going to take upper-division electromagnetism course. The text for the course is Griffiths' Introduction to Electrodynamics. I am not a physics major (I am a math major), but I have taken the first-year, calc-based physics sequence...
  35. MTd2

    M-Theory as an anyonic electromagnetism?

    I was reading about M2 branes these days and I found out that the special thing about the BLG 3-algebra it is that they relate branes to a chern simons dual-quiver tiling of the torus: http://www.nonequilibrium.net/381-m2-branes-chernsimons-theories/ Non abelian anyons are one of the...
  36. S

    How Does the Biot-Savart Law Apply to a Square Loop in a Plane?

    Homework Statement A square loop of wire C, with side length 2a lies in a plane P and carries a steady electic current I. By using the Biot-Savart law show that the magnetic field B(r) at any point r in P but not in C is perpendicular to the plane P. Calculate the magnetic field at the...
  37. E

    Maximum producible energy (electromagnetism; cyclotron)

    This isn't exactly homework, but I felt that I had too much to ask that it wouldn't be right to put this in the regular section. Anyway, I've been reading the original paper on the design of a cyclotron (Lawrence & Livingstone) and there were two parts which didn't agree with what I knew... and...
  38. J

    Gravitation and electromagnetism is unified by Kaluza-Klein theory

    Recently I read that gravitation and electromagnetism is unified by Kaluza-Klein theory. Can someone tell me in depth how they are unified
  39. P

    Electromagnetism Explaining Question

    1. The problem statement, all given/known data A bar magnet is positioned at the mouth of a solenoid. The current indicated in the solenoid is then turned on. (Assume the solenoid is a lot bigger than the bar magnet.) Gravity and friction can be ignored. Describe what would happen, and...
  40. N

    Supplementary Textbooks for Electromagnetics & Thermodynamics

    Can anyone recommend supplementary texts books for Electromagnetism and Thermodynamics? I'm looking for some alternatives to my recommended textbooks. The first class is an electromagnetics class. This class is heavily calculus based and consists of building up concepts that culminate to...
  41. I

    Schaum's outline of Electromagnetism

    I am studying for my junior level EM final that is a few weeks from now, we are using Griffiths' Introduction to electrodynamics. To prep for the test I am already planning on working through all of our homework problems, and examples in relevant sections, as well as a few problems we didn't do...
  42. P

    A galilean puzzle in electromagnetism

    A "galilean puzzle" in electromagnetism Well, I still didn't managed to find the answer, since the puzzle seems a little bit more involved than I first tought...to perform the computations, you only need to know a little bit about lagrangian/hamiltonian dynamics in electromagnetism. Consider...
  43. C

    Electromagnetism calculation help

    1. An electron is traveling in the +ve x-direction of an inertial frame T. An acceleration is given to the electron in the +ve y-direction with as large as magnitude as possible. How do I specify directions of the electric and magnetic fields that will achieve this? Why are the choice...
  44. snoopies622

    Is Special Relativity Consistent with Classical Electromagnetism and Mechanics?

    I thought I understood this matter, but the more I think about it the more confused I am becoming. Suppose I have a very long wire which has a uniform negative charge per unit length ρ. I hold near it a particle with charge -q. Due to the electrical field around the wire there is a force...
  45. S

    Feynman's apparent paradox - Electromagnetism

    Feynman's "apparent" paradox - Electromagnetism This is the paradox discussed in chapter 17 of "Feynman Lectures on Physics - Vol II" http://www.flickr.com/photos/37453425@N07/3447068420/ Say suppose the battery drains out or somehow you stop the current outta the battery. By...
  46. F

    Has Electromagnetism Shaped Cosmic Structures?

    Is there any evidence that electromagnetism has played a role in the formation of galaxies, galactic clusters, and super cluster filaments?
  47. Phrak

    Action at a Distance in Electromagnetism?

    Maxwell's equations in integral form are not obviously local. Faraday's Law, a good enough example, in differental form is \partial_i B_j - \partial _t E_k = J_k where (i,j,k) are cyclic permutations of (x,y,z). In integral form, \frac{d\Phi}{dt} = \oint E \cdot dl The...
  48. Phrak

    Three Laws of Classical Electromagnetism

    I believe classical electrodynamics can be reduced to: 1) Lorentz force 2) Existance of a Lorentz invariant vector field of real entries, V=V^\mu \hat{e}_\mu 3) Charge is always associated with mass Maxwell's equations are obtained by associatating elements of the vector field with...
  49. L

    Electromagnetism - particle moving in magnetic field

    A amssive charged particle moves under the influence of a time varying magnetic field \mathbf{B}=B(r,t)\mathbf{\hat{z}}, where r is the distance from the z axis. Show that the particle can move in a circular orbit in a plane perpendicular to the field, accelerating and decelerating under the...
  50. C

    Is Electromagnetism Relative and Does it Create a Paradox in Moving Frames?

    Correct me if I am wrong, but, if electromagnetism is relative then in a frame where charges have relative motion between the observer, the observer would detect electromagnetic radiation being emitted from the charge, and that to an observer moving alongside the charge at the same speed, no...
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