What is Electricity and magnetism: Definition and 212 Discussions

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. M

    What is the net force on the current loop?

    The long wire carrying ##5A## current causes a non-uniform magnetic field whose formula is known. I calculated the force exerted by this magnetic field on each of the four sides of the rectangular loop and summed them up. I got the right answer, but a question is nagging me---doesn't the loop...
  2. O

    Understanding the energy of a dipole in a uniform electric field

    Griffith's E&M problem 4.7 asks to calculate the energy of a dipole in a uniform electric field and I ended up getting a different answer than the one given. I thought that calculating the energy/work done to construct the dipole is the same as dragging two point charges where one is d apart...
  3. S

    Solid State Researching Gold Thin Films: Electrical & Optical Properties

    Hi Physics folks,I am currently collecting resources for my senior seminar project at my university and would like to ask if anyone has any good references for gold thin films. I am planning on focusing primarily on the electrical and optical properties of gold thin films. I appreciate any...
  4. dliu1004

    Question on a Gauss's Law problem

    Summary:: I understand the basics of Gauss's Law and how to solve some of the simpler problems, but I cannot seem to solve these two questions. For question 007, one of my friends told me I had to ignore the outer shell? I did that: I integrated rho dV: (6.02*r*pi*r^2*h) from r=0 to r=.0462...
  5. B

    Show that Faraday's Law holds

    I've calculated the negative time derivative of B(r, t) as: $$-\frac{\partial B}{\partial t} = k~\text x~E_0~\text{sin}(k \cdot r - \omega t + \phi)$$ The cross product can be easily expanded, I'd just rather not do the LaTeX for if I can avoid it. The Curl of the electric field...
  6. Viona

    A Current-Carrying Conductor

    Hello, In the section of Magnetic Force on a Current- Carrying Conductor in the book of College Physics by Serway, it is written that the Current- Carrying Conductor in a magnetic field deflects because the magnetic force on the electrons transfers to the bulk of the wire due to the collisions...
  7. P

    Solving Part e of the Electron Beam Problem

    I am only asking about part e. If you are short on time, you can read through parts a - d, to get an idea of what is happening, and then attempt part e directly. I have solved parts a - d. If you would like to check your answers, the answer to part c is [rne^2 / 2e0] [ 1 - (v/c)^2], and the...
  8. P

    Principle of superposition for charges/induced charges

    The key observation to solve the above problem is that the charge Q can be dragged out into a flat capacitor plate parallel to the 2 existing plates. Apparently, while the charge distribution on the 2 existing plates changes, the total charge induced on each plate remains the same, due to the...
  9. yyfeng

    Simple Electric Field due to a Charged Disk

    My attempt at a solution is shown in attached file "work for #10.png". I used Desmos Scientific online calculator to obtain my final answer.
  10. P

    Position for maximum electric field between two wires

    For the first part, since $$ E(r) \propto \frac{1}{r} \hat{r}$$ by the principle of superposition the maximal electric field should be halfway in between the two wires. Then I'm not sure how to go about the second part of the question. I understand that the total potential due to the two wires...
  11. P

    Divergence of a radial field ##F=\hat{r}/r^{2+\varepsilon}##

    Following (1), \begin{align*} \text{div} F = \vec{\nabla} \cdot \vec{F} &= \frac{1}{r^2} \frac{\partial}{\partial r} \left( r^2 F_{r}\right) \\ &= \frac{1}{r^2} \frac{\partial }{\partial r} \left( r^2 \frac{1}{r^{2+\varepsilon}}\right) \\ &= \frac{1}{r^2} \frac{\partial}{\partial r}...
  12. tanaygupta2000

    Resultant field at the center of two semicircular current arcs

    So the magnetic field induced at the center of a current-carrying loop is given by: B = μ0 i /2r where r is the radius of the loop In the case of a semi-circular loop, this becomes B = μ0 i /4r In the question, i = 2A, r1 = 1m and r2 = 2m So, field induced at the center of first semicircular...
  13. Luke Tan

    Charge Inside a Cavity in a Conductor

    Let us say we have a cavity inside a conductor. We then sprinkle some charge with density ##\rho(x,y,z)## inside this surface. We have two equations for the electric field $$\nabla\times\mathbf{E}=0$$ $$\nabla\cdot\mathbf{E}=\frac{\rho}{\epsilon_0}$$ We also have the boundary conditions...
  14. T

    Calculating E-field Through Layers w/ Diff. Permittivities & Conductivities

    I'm trying to understand how the total electric field changes as it passes through layers with different electrical permittivities and conductivities (as shown in the linked figure). The rectangular prism layers are assumed to be very thin. The conductivities ##\sigma## and relative...
  15. H

    Electric field from a charge q1

    Hi, I have a charge q1 = -10 * 10^9. The the coordinatesare (3,4)m. I found the electric field vector that is (-2160i -2880j) n/c. My questions is if I add a charge q2 to the the coordinates(0,0) is the electric field stay the same?
  16. S

    Force on a copper loop entering into a magnetic Field B with speed v

    Hi, second problem in one evening, I'm sorry! But I'm also not quite sure if I did this one right. I had thought I need lenz's law but there is no current before entering the field so I just use the induced Voltage? My approach: ## V = \frac {B*A}{t} ## ## IR = \frac {B*A}{t} ## and ## A = v*t...
  17. Hawkingo

    What are some good books on electricity and Magnetism

    Can someone please suggest some good books on electricity and Magnetism for graduation in physics? Thanks for helping:smile:
  18. Taxi1337

    Sphere-with-non-uniform-charge-density ρ= k/r

    I am working on the same problem as a previous post, but he already marked it as answered and did not post a solution. https://www.physicsforums.com/threads/sphere-with-non-uniform-charge-density.938117/ I am curious as to a method of finding the ##k## and substituting into the electric...
  19. Zack K

    Final potential difference of a 2 capacitor system

    Homework Statement An isolated parallel-plate capacitor of area ##A_1## with an air gap of length ##s_1## is charged up to a potential difference ##\Delta V_1## A second parallel-plate capacitor, initially uncharged, has an area ##A_2## and a gap of length ##s_2## filled with plastic whose...
  20. P

    Wire surrounded by a linear dielectric in a uniform E field

    Homework Statement We have an uncharged, conducting wire with radius a. We surround it by a linear dielectric material, εr, which goes out to radius b. We place this in an external electric field, Eo. Homework Equations We have electric potential inside (a < s < b) Vinbetween=Acosφ +...
  21. P

    Calculating the electric potential

    Homework Statement We have the cross section of a metal pipe that has been split into four sections. Three of the sections have a constant electric potential, Vo. The fourth section is grounded so electric potential is zero. We are looking for electric potential inside and outside of the pipe...
  22. Silentwhale

    Electricity and magnetism (Gauss' law)

    Homework Statement Given two things spherical shells radii r1 and r2 with r2 > r1. The inner she'll is charged uniformly with a total charge Q1, while the outer shell with Q2. A) use gauss law to computer the electric field everywhere B) Use any method to calculate the potential everywhere...
  23. Silentwhale

    Electricity and magnetism: Electric Field for Two Long Charged Lines

    Homework Statement Given two very long lines each is charged with linear density +lambda Coulombs/meter. The two lines are separated by a distance of d metres. A) show the electric field E, at any point along one of the lines due to the other line is E = lambda/(2 (pi)(epsolon o)(d)) (Note...
  24. starstruck_

    Electric field of spherical shell

    Homework Statement Consider a spherical shell with uniform charge density ρ. The shell is drawn as a donut with inner (R1) and outer (R2) radii. Let r measure the distance from the center of the spherical shell, what is the electric field at r>R2, R1<r<R2, and r<R1. I am working on the r > R2...
  25. starstruck_

    Calculating total Coulomb force vector ?

    Homework Statement Consider a configuration consisting one +q charge ( upper right) and three −q charges, arranged in a square. Side lengths = d. Calculate the total F force vector acting on charge +q.Homework Equations Vector form of culomb’s force F=( kq1q2/r^2) rhat (rhat for unit...
  26. starstruck_

    Infinite chain of alternating charges (+/-)

    Homework Statement A crystal is a periodic lattice of positively and negatively charged ions. (a) Consider an infinite one-dimensional crystal of alternating charges +q and −q, separated by distance d...
  27. shahbaznihal

    Testing Electricity and Magnetism section in GRE Physics

    Hi, I am taking GRE Physics this year and I am preparing from Conquering GRE Physics book and I have covered everything in that book on Electricity and Magnetism (yet to study Optics and Waves). My question: How much from Griffith Electrodynamics book do I need to study? Or is the material in...
  28. A

    Electricity and Magnetism Electric Field Problem

    1. Problem Statement: Find positions on the x-axis for the charges Q1 = -1 C and Q2 = +3 C so that the electric field is zero at x = 0. Homework Equations :[/B] I'm thinking I need to use Coulomb's law for this one. I'm just having trouble figuring out where to start. Coulomb's states E=kQ/r^2...
  29. starstruck_

    Some good physics educators on youtube?

    HI! I'm in first year physics right now doing the second part of my course - electricity and electromagnetism, and I'm REALLY struggling. This is mostly due to the fact that other than very basic, grade 11 circuits, I had no base going into electricity for first year physics because my teacher...
  30. Gene Naden

    Classical Looking for a textbook of undergrad E&M, for Physics Forum Help that I give

    I sometimes post answers to threads people post about E&M. Unfortunately, my Masters in physics was 40 years ago and I am a little rusty. I am looking for something that will help me answer people's questions. The level of math can be fairly sophisticated as I have brushed up a bit.
  31. F

    I Please suggest whether I should use delta or dx method.

    I previously made a derivation of Neumann potential. It can be found in the pdf file below. I originally made it in the ##dx## method. It involved equations like ##dm=I dS##. My maths teacher told that such an expression has no meaning, at least in elementary calculus. However I argued that my...
  32. M

    Fun magnetics question with the Meissner Effect

    I was hoping I could get some help deriving a formula that shows how much current is needed to generate enough of a magnetic field to lift an X Newton mass L meters above a superconductor. ( Probably in centimeters but meters here for the sake of SI easiness ) I was helping one of my professors...
  33. Fraser MacDonald

    What is the electrostatic force field?

    I have just covered the electricity unit in my advanced higher physics course, and have happily accepted that a force is created between charged particles. I understand that coulombs law can be used to calculate this force, but here is my question. What actually is this force between the charged...
  34. astrocytosis

    Radial force on charged particle in beam of positive ions

    Homework Statement Many experiments in physics call for a beam of charged particles. The stability and “optics” of charged-particle beams are influenced by the electric and magnetic forces that the individual charged particles in the beam exert on one another. Consider a beam of positively...
  35. S

    Resistors in Series - Lab data confusion

    Homework Statement (see my attached photo to better understand where I am coming from!) So after some research, I've discovered that the current at different points in a simple series circuit is supposed to be the same value, and that the voltage is supposed to be different values. I...
  36. S

    Resistors in Series - Lab data confusion

    Hi guys! (see my attached photo to better understand where I am coming from!) So after some research, I've discovered that the current at different points in a simple series circuit is supposed to be the same value, and that the voltage is supposed to be different values. I performed a lab on...
  37. L

    Is average time between and after collision same for a gas?

    I am stuck on this concept in my physics book where the author claims that in a low density ionic gas the average of the time between collision and average of the time taken from last collision in ions is same. He further states that the average time to the next collision is same as the average...
  38. A

    Draw field lines for both magnetic fields

    Homework Statement Homework Equations N/A The Attempt at a Solution Im not sure if I've done this right because it seems too little for 6 marks. I have arrows coming from the north to the south end for the magnet's magnetic field. I have arrows going counter clockwise around the conductor...
  39. C

    Help: Electricity and Magnetism Question

    Two long, parallel wires are separated by a distance of 1.0m. The current in each wire is 1.0A. What is the magnitude of the force on 1.0 m length of each wire? Help~ Thanks a lot
  40. J

    Electric Field and Potential Scenario

    Homework Statement I was wondering in what situation would the potential and the electric field of the system both be equal to zero at the same time? Homework Equations W=-ΔU=-ΔVq ΔV=-∫Edr V=kQ/r (with reference r->∞) The Attempt at a Solution I know for the middle of a dipole the potential...
  41. egio

    I Not sure what I can make into equivalent resistors

    Could I combine the two resistors together in parallel to make an equivalent resistor, and then use that equivalent resistor in series with the capacitor? It would be great if there was some rule of thumb that I can use to know what I can make into an equivalent resistor/capacitor down the line...
  42. V

    Find electric potential of field inside and outside nucleus

    Homework Statement Derive following expression for the electrostatic potential energy of an electron in the field of a finite nucleus of charge, ##+Ze##, and radius, ##R=r_0A^{1/3}##, where ##r_0## is a constant. (Charge density is constant.) The potential we are asked to derive is: $$ V(r) =...
  43. lz975545

    Electric potential at the bottom of a ring?

    Homework Statement [/B] A circular ring of radius "a" has a total charge Q uniformly distributed along the top half. (Q is distributed along the semicircle in quadrants I and II). What is the potential at a point located on the bottom of the ring (observation point is on the ring in quadrant...
  44. bananabandana

    Relativistic Lagrangian

    Homework Statement Show that $$ \mathcal{L} = -\frac{1}{4}F^{\mu \nu}F_{\mu \nu} = - \frac{1}{2}\partial^{\mu}A^{\nu}(\partial_{\mu}A_{\nu}-\partial_{\nu}A_{\mu}) $$ Where $$ F^{\mu \nu} = \partial^{\mu}A^{\nu} - \partial^{\nu}A^{\mu} $$ Homework EquationsThe Attempt at a Solution $$...
  45. N

    Discontinuities in the time derivative of the magnetic field

    An inductor and resistor are arranged in parallel to a constant voltage source. There is a switch connected to a terminal on the inductor that can create a closed loop that includes either the voltage source, or the resistor. The switch is left connecting the source and inductor for a long...
  46. M

    Radio Broadcast Antenna Peak Intensity

    Homework Statement A radio broadcast antenna is located at the top of a steep tall mountain. The antenna is broadcasting 104.3 FM (in Megahertz) with a power of 5.00 kilowatts. What is the peak intensity of the signal at a receiving antenna located 25.0 km away? Homework Equations Honestly...
  47. G

    Proving that torque is m X B

    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...
  48. 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...
  49. 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...
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