Electricity and magnetism Definition and 215 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. G

    How Does Torque Relate to Magnetic Dipole Moment in Physics?

    Homework Statement Starting from the Lorentz force law, in the form of Fmag = ∫ I (d× B), show that the torque on any steady current distribution (not just a square loop) in a uniform field B is m × B. Homework Equations I looked at the solution I found in this thread here, but I don't...
  2. M

    Concentric Coils EMF from Graph

    Homework Statement Two concentric circular coils of wire lie in a plane. The larger coil has 61 turns and a radius of a = 7.40 cm. The smaller coil has 58 turns and a radius of b = 0.95 cm. The current in the larger coil has a time dependence as shown in the figure. Picture and graph...
  3. NiendorfPhysics

    Radius of Half Electric Potential Energy

    Homework Statement There is a solid cylinder of radius a and then empty space then a shell cylinder of radius b. Show that half of the stored potential energy lies within a cylinder of radius $$\sqrt{ab}$$ Homework Equations In the attempt The Attempt at a Solution I'm not sure what they...
  4. E

    Calculus Updating my Electricity and Magnetism --> Vector Calculus?

    Dear all, I'n an EE that finished his degree more than 10 years ago. I wanted to refresh my Electricity and Magnetism knowledge. I bough Purcells book some weeks ago (https://www.amazon.com/dp/1107014026/?tag=pfamazon01-20) and I'm kind of struggling through the maths (Vector calculus). I've...
  5. 1

    Electric field of a charged dielectric sphere

    Homework Statement A dielectric sphere of radius R with uniform dielectric constant ε has an azimuthally symmetric density charge σ = σ0 cos θ placed on the surface. Outside the sphere is vacuum. (a) Obtain the electrostatic potential inside the sphere, φin. (b) Obtain the electrostatic...
  6. K

    RMS Current through RLC combination ciruit

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  7. Jabbar

    Electric field due to a charged rod

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  8. peasqueeze

    I Use Lorentz Force to Find Magnetic Field Components

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  9. J

    Classical Panofsky VS Nayfeh on "Electricity and Magnetism"

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  10. U

    Why the efficiency of air core transformer changes (up and down)

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  11. NicolasPan

    Find the electric field of a uniformly polarized sphere

    Homework Statement We want to calculate the field of a uniformly polarized sphere of radius=R Homework Equations V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \oint_{S} \frac{\sigma_{b}}{r} da' + \int_{V} \frac{\rho_{b}}{r} d\tau' The Attempt at a Solution i)I know that \sigma_{b} = P...
  12. Raul Trejo

    Fractioned electrons, what do they mean?

    Homework Statement Excess electrons are placed on a small lead sphere with mass 8.00g so that it's net charge is -3.20x10^-9C (a) Find the number of excess electrons on the sphere. (b) how many excess electrons are there per lead atom? The atomic number of lead is 82, and its atomic mass is...
  13. RoboNerd

    Classical Good self study book for Electricity and Magnetism

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  14. bananabandana

    I Confusion With Derivation of Fresnel Equations

    Okay, so I'm working with the diagrams above. ##i## denotes incident, ##r## reflected, and ##t## transmitted. -We're working in two HIL dielectrics. Incoming and outgoing waves are of form ##Aexp[i(\vec{k}\cdot\vec{r}- \omega t) ##. As I understand it, Maxwell's equations give four boundary...
  15. Z

    Proving an expression / help with defining electric current

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  16. A

    What does current density mean?

    Homework Statement Current density is the amount of current per cross sectional of flow. I'm having trouble wrapping my head around this definition. Surface charge or volume charge I understand better since they are almost analogous to the density we all understand (amount of matter/charge...
  17. 1

    Calculating voltage between two points....

    Homework Statement Homework Equations The voltage between any two points due to the field from a point charge q is: Kirchoff's voltage laws, which states that the total voltage around a closed loop must be zero, i.e.: The Attempt at a Solution To find V(e<-d) I used Kirchoff's...
  18. Elvis 123456789

    Magnetic Field at the center of a square loop

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  19. Elvis 123456789

    Magnetic Field at center of a Square loop

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  20. W

    Capacitors in Series and Parallel

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  21. B

    Angle of electric field line heading to infinity

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  22. P

    This formula is applicable for a point charge distribution.

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  23. D

    Balancing Electric and Gravitational Forces Between Two Objects

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  24. A

    Testing the strength of an electromagnet....

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  25. R

    (Simple Electromagnetics) A charge placed between 2 charges

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  26. D

    Question about Purcell - Electricity and Magnetism

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  27. Shashank Verma

    Understanding Electricity and Magnetism: Solving Practice Problems

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  28. S

    Intro Physics EM Theory Books: Find Textbooks to Enhance Learning

    Hello, Am starting to read Electromagnetic Theory. Can you suggest some good textbooks on the topic that will help clear the concepts. Thanks in advance
  29. Anode

    Torque on a Disk in a Magnetic Field (E&M)

    Hi, I've been struggling on this homework problem for quite a few hours now and would really appreciate a pointing in the right direction. It's a fairly entertaining problem that I'm getting stuck on in several places. 1. Homework Statement The problem goes: "An erratic engineer, who lives in...
  30. P

    Electric Fields in Coaxial Cables: Understanding Bound Charge Densities

    Homework Statement http://postimg.org/image/vzhqi8er5/ Homework EquationsThe Attempt at a Solution I understand all the calculations here - http://www.physicspages.com/2012/10/18/coaxial-cable-with-dielectric/ I have one issue that is bugging me though - if λ charge density is distributed over...
  31. P

    Conductor in a capacitor problen (E&M)

    1. The question: This question is from purcell's E&M book (3.71). (a) The plates of a capacitor have are A and separation s (assumed to be small). The plates are isolated, so the charges on them remain constant, the charge densities are +-σ. A neutral conducting slab with the same area A but...
  32. Scott Hill

    Intro Physics A new online introductory E&M textbook (in progress…)

    Hi! I am writing a calculus-based HTTP://textbook.scotthill.us. It is an HTML-based book with animations, interactive demos, quizzes, and so forth. The first draft is almost complete (I still have to write chapters on integration, induction, and wave optics), but I wanted to share it with a...
  33. Kerrigoth

    Calculating multiple magnitudes for induced electric field

    Let's say I place two different size conducting loops inside of a uniform magnetic field. For the sake of the diagram I have the loops share a point, but just treat them as though they are not touching. Then I decrease the value of the magnetic field very quickly. \frac{dB}{dt} =...
  34. I

    Physics graduate in need of career advice

    Hello, my name is Israel and I have a B.A. in physics from California State University Stanislaus. I graduated in 2011 in the worst economy ever and in the worst part of the U.S. to be hit by the great recession. I have substitute taught in every subject in K-12, but I am looking to get into the...
  35. B

    Problem with Net Coulombic Force

    Homework Statement Consider an ## n ##-dimensional solid sphere of radius ##R##, with uniform charge-density and a total charge ##Q##. A charged particle ##q## is kept at a distance of ##r## from the center. For ##r<R##, what is the Net Coulombic Force experienced by the particle? If it is in...
  36. R

    Electricity and Magnetism RC Circuit Conceptual Questions

    Edit: sorry i realized i posted this in the wrong section. Can some move it to hw? Thank you. Hey i was studying intro E&M recently and i started learning about RC circuits. Up until this point everything, concept wise, has made sense for me. Then I learned how RC circuits work, and the math...
  37. Kerrigoth

    Are induced currents created by motion or change in flux?

    The book I am working through is beginning to dive into induced currents and Lenz's Law. When a conductor is moving perpendicular to a magnetic field, the charge carriers inside will experience a magnetic force; This causes the charges to move. Eventually, the electric field from the charge...
  38. EddieP

    Magnetic field around a wire near ferrous materials

    I was wondering if I could ask a question on the magnetic field surrounding a current-carrying wire, and how this field might change with the presence of other, ferrous materials nearby. I have been using this web page http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c3 to...
  39. Kerrigoth

    Series capacitors and the amounts of charge on the plates.

    First in Circuit A: I hook up a battery with a voltage of V up to a capacitor C1. Once C1 is fully charged it has 6+ on its positive plate and 6- on the negative plate. Given it's fully charged, the +terminal of the battery and the +plate are in electrostatic equilibrium. Since they are both in...
  40. EddieP

    Increasing the magnetic field around a wire

    I am interested in calculating the magnetic field around a wire. Using the formula found here http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html#c3 I can calculate that B = (μ0*I)/(2*pi*r) Where I equal current in Amperes, and r equals distance from the wire in meters. This gives...
  41. T

    Classical Best intro physics (electricity and magnetism) for freshman

    I took a college physics course (Mechanics) at a CC, and my physics prof was notoriously known to be one of the best... many of the students transferred to Berkeley and say that he is one of the best they have taken. He said that his two favorite book are: Halliday Resnik: Fundamentals of...
  42. kelvin490

    Understanding MMF in Transformer

    I am studying about transformer and get confused about some concept. I have learn that in an ideal simple transformer the primary has two components of current: Magnetization current i.e. the open-secondary primary current. Current that (ignoring small leakage inductances) finds it way (via...
  43. C

    Intro Physics Best books on electromagnetism, electricity and magnetism?

    Hi, I'm looking for some great books clearly explaining how electricity, magnetism and electromagnetism Works. I'm also looking for some books describing how it was discovered and what experiments have been performed in discovering how it Works,. So Far I've looked at Electromagnetism...
  44. N

    Integral Form of Gauss' Law at Center of Finite Wire

    At the exact center of a finite wire (i.e. a distance, say $L/2$ from each end), why can I not apply Gauss's Law in integral form to find an EXACT solution for the electric field? At the center of the wire, $E$ is entirely radial, so it seems like I should be able to draw an infinitesimally...
  45. Crystal Pearl

    Schools Can I take Electricity and Magnetism in grad school

    I am supposed to graduate next year but I just realized I have left Electricity and Magnetism off of my schedule. I'm afraid to add it because I feel like I am already taking enough and I am wondering if instead it is common or likely to just take the undergrad elective in graduate school. I...
  46. akashpandey

    Relation between electricity and magnetism?

    Why flowing current in wire creat magnetic field...if anybody say this is because of spin quantum number,... So i just want to say spin quantum number is because of wave nature of electron.i just want to know what effect of dual nature of electron on magnetic field.:rolleyes:
  47. 2

    Back emf in a single loop of wire?

    I have been thinking about coils of wire carrying alternatingcurrent. From what I understand, a back emf is induced in the coil because there is a changing magnetic field around each individual loop of wire, and therefore there is a changing flux through each loop because the changing field...
  48. 2

    Do back force and back emf come together?

    i have heard it said that back force occurs in generators and back emf occurs in motors, however I was considering a motor and I thought that it seems to me that as the coil is rotating and it has the changing flux linkage, and thus a back end is induced in it by Lenz's law, this reduces the...
  49. NoSniping

    What Inductance Value Is Needed for a Light Bulb in a 240V AC Circuit?

    Homework Statement How large an inductance should be connected in series with a 120 volt (rms), 60 watt light bulb if it is to operate normally when the combination is connected across a 240 volt, 60 Hz line? (First determine the inductive reactance required. You may neglect the resistance of...
  50. hackhard

    Electromagnet to attract small iron pieces

    i want to build an electromagnet which can attract small iron pieces(2-3 mm long) at a distance of 10 cm from the magnet.I am using 24 awg. magnet wire.Please help .answer these questions - 1) How long magnet wire (24 awg) do i need? 2)How much current 3) what shud be least radius of solenoid 4)...
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