Field Definition and 1000 Threads

  1. G

    I Quantum field theory: an informative approach

    I'm looking for a book that describes the quantum field theory without going deeply in the theory with formulas or complex description of the mathematics under the theory. I know that this theory is really complex and it needs a deep knowledge of quantum physics in order to be understood. But...
  2. jisbon

    Electric field of an infinite charged plate

    So I figured to get e-field at point (4,4,0), I need to find the resultant e-field from the negatively charged particle and the plate ##E_{resultant}=E_{particle}+E_{plate}## ##E_{particle}=\frac{kq}{d^2}=\frac{(9*10^9)(-2*10^-6)}{4^2}=-1125N/C## Now for the plate is where I'm confused. If this...
  3. D

    Amplitude of an oscillating electric field

    Homework Statement: The amplitude of the oscillating electric field at your cell phone is 4.0 μV/m when you are 10 km east of the broadcast antenna. What is the electric field amplitude when you are 20 km east of the antenna Homework Equations: electric field i've done E=##\frac A...
  4. ChrisXenon

    I E & B field phase relationship in EMR

    Common diagrams for the magnetic and electric field components of EMR show the fields at right angles in space with peaks aligned along the axis of propogation, for example Wikipedia here: https://en.wikipedia.org/wiki/Electromagnetic_radiation. However, Faraday's law says the E field depends...
  5. warhammer

    Classical Physics & Particle Motion Under Force Field

    The particle is moving under a force field with the potential energy equation described above. I find it logical that Newton's Laws can be used as in the question itself it is stated that the velocity is quite small and we could approximate its subsequent motion via the notions of Classical...
  6. bob012345

    Energy vs. Time in a Magnetic Field due to a Current Carrying Wire

    I want to know the total energy contained in a magnetic field due to a long wire (just consider a 1m segment) as a 1amp current is turned on starting at time zero. I'm assuming zero turn-on time for convenience. At t=0 the cylindrical field is formed and I wish to know the total energy as a...
  7. D

    Electric field in the narrow wire

    i've started from this I1=I2 then I1= JA1=##\frac {E l} R## I2= JA2=##\frac {E_2 l} R## but can't get anything useful relating them. Am i forgetting any other useful formula? I get as result E4
  8. A

    Electric Field for the circular path of a positively charged particle

    Here is picture. Answers is A. My attempt was that I thought if i were to place a positive test charge then it would go from top to bottom if there was a positive charge in the center it was avoiding and a positively charged particle at the top, but an electron at the bottom so it would avoid...
  9. D

    The distance where the magnetic field of two wires is zero

    Homework Statement: The distance between two parallel long wires, carrying currents equal to i and 3i respectively, is d as shown in the picture. What is the distance from the wire carrying the current i at which the magnetic field is zero Homework Equations: guess biot-savarat Being two...
  10. C

    Is the Electric Field Calculation Consistent with the Potential Result?

    Question Part C Part D
  11. C

    Deriving an Expression for an Electric Field along the Z axis

  12. TheBigDig

    Derive an expression for the applied field of a superconducting wire

    So far the best I've been able to come up with is to use ##\vec{B} = \mu_0 \vec{H}## which gives me i_c = H 2\pi r j_c = \frac{H 2\pi r}{\pi r^2} = \frac{2H}{r} \therefore B = \mu_0 \frac{r j_c}{2} I'm fairly confident this is just terrible math and physics on my behalf but I'm struggling to...
  13. M

    How to characterize a power law field?

    Hello, as part of the study of fields with central forces, I came across with fields called power law, defined by F = - K/r ^ n u (u is radial vector passing through the origin O) I would like to dismiss case n = 2, which refers to the Newtonian fields whose study was exhaustively conducted in...
  14. S

    Find the speed of a copper loop falling in a magnetic field

    Hi all, so I had this problem and on the exam and I got a solution but I had an mass-term in there which wasn't given. I used Farraday's Law of Induction to get the Voltage induced. Then I used ##rho* \frac{A}{4a} ## for the resistance and divided the Voltage by that to get the current. I then...
  15. Yalanhar

    Electric Field due a charged disk

    Homework Statement: uniformly charged disk, radius r, with surface charge density ##\sigma## . I want to find the electric field along the axis through the centre of the disk at a h distance Homework Equations: ##dE=\frac {kdq}{r^2}## My Solution: ##dE=\frac {kdq}{r^2}## in this case r=s...
  16. Yalanhar

    Calculate the electric field due to a line of charge of finite length

    Homework Statement: A thin rod of length L and charge Q is uniformly charged, so it has a linear charge density ##\lambda =q/l## Find the electric field at point where is an arbitrarily positioned point. Homework Equations: ##dE=\frac{Kdq}{r^2}## A thin rod of length L and charge Q is...
  17. Q

    A Explicit form of annihilation and creation operators for Dirac field

    I'm unclear on what exactly an annihilation or creation operator looks like in QFT. In QM these operators for the simple harmonic oscillator had an explicit form in terms of $$ \hat{a}^\dagger = \frac{1}{\sqrt{2}}\left(- \frac{\mathrm{d}}{\mathrm{d}q} + q \right),\;\;\;\hat{a} =...
  18. AndresPB

    Electric Field from its Potential of a Half Circle along its Z axis

    So I figured out the potential is: dV = (1/(4*Pi*Epsilon_0))*[λ dl/sqrt(z^2+a^2)] . From that expression: We can figure out that since its half a ring we have to integrate from 0 to pi*a, so we would get: V = (1/(4*Pi*Epsilon_0))*[λ {pi*a]/sqrt(z^2+a^2)] In that expression: a = sqrt(x^2+y^2)...
  19. V

    Solid State Textbook on crystal field theory and degeneracy breaking

    In particular I would like to have a resource for the relation between group theory, crystal field symmetries and breaking of degeneracies of orbitals. I've taken a graduate condensed matter course and graduate quantum mechanics courses. I have some basic knowledge of group theory but can learn...
  20. N

    Find the Electric Field E using Gauss' Law

    I tried to work out both a) and b), but I am not sure if I am correct. I drew a picture with a sphere around q first with radius r and then with radius 3r. For a) ##E.A=\frac {q}{ε_°}## (when using Gauss' Law) Since ##A=4πr^2##, I substituted this in the equation and solved for E giving me...
  21. K

    I Field theories in 4 dimensions

    Hello! I know this is a very general question (and I am really a very beginner in the field) so I am sorry if it is dumb, but here it goes. In Schwarz book on QFT, at the end of Section 14.4 (path integrals chapter) he says: "We do not know if QED exists, or if scalar ##\phi^4## exists, or even...
  22. Dan13

    How to interpret magnetic field diagrams?

  23. M

    I Why does quantum mechanics believe that gravity is a field?

    According to general relativity, gravity is simply the side-effect of bending the geometry of space-time. As a thought experiment imagine a 3D image being projected from a 2D hologram - the distance between the actual 2D pixels in the 2D plane always remains constant, yet depending on the shape...
  24. D

    Does an AC Magnetic field induce movement in a DC Magnetic Field?

    Summary: Can a rotating AC Magnetic field induce movement in a static DC Magnetic flux? I'm designing a control panel, and the customer has asked us to reduce the EMC as much as possible; there are no drives, or other noise creating devices, just AC circuits. I thought a good starting point...
  25. R

    Derivation of ideal magnetic dipole field strength

    For reference, this is from Griffiths, introduction to quantum mechanics electrodynamics, p253-255 When deriving the ideal magnetic dipole field strength, if we put the moment m at origin and make it parallel to the z-axis, the book went from the vector potential A $$ A=...
  26. B

    Electron helix in a magnetic field

    I thought that a nearly parallel entry path would result in a helix of very small, but constant, radius. I would not expect the electrons to focus at a point, but continue along the infinite helix. What have I missed?
  27. adamaero

    By using Gauss' law, can the electric field be p/(pi*ε*r^2)

    Which is better to use? The equation for the area or the circumference of a circle? Schaum's Electromagnetics (4 ed) by Edminister vs http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecyl.html
  28. S

    Electric field due to two positive charges

    I am having trouble solving the following problem. I am given two positive charges on the x axis: I know that the electric field strength at point P is ##E=150 \frac{V}{m}##, ##d=1.8m## and ##a=2.5m##. I want to find the charge of ##Q##. As far as I know, the electric field on the y-axis...
  29. Alfredo Tifi

    Synchrotron Radiation: Charge Loss of Relativistic Particles in Magnetic Fields

    Problem Statement: It is possible to describe synchrotron radiation as caused by a loss of electrical charge of relativistic particles that are moving in a magnetic field? Relevant Equations: E = mc2 An Italian expert of black hole M87 (Elisabetta Liuzzo) explains that the expected axial...
  30. R

    Electric field on a ring's axis

    The contribution coming from a little segment of the ring is ##d\vec{E}=\frac{dQ}{r^2}cos\theta \hat{z}##, assuming that the horizontal components cancel out. But how can we show that?
  31. L

    I have finally re-entered the IT field yesterday

    Hi, I just got an IT Internship at a local nonprofit. It sounds like it will be a mid-high-level desktop support position. I will be imaging computers and that's all I know so far. I start ASAP and they're processing the paperwork as I speak. Anyway, I haven't worked in IT since 2017 and now I...
  32. D

    I Earth’s Magnetic field formula or downloadable vector field

    I want to render the Earth’s Magnetic field in a software and simulate solar wind electron interaction with it. How do I calculate the magnetic strength and vector orientation at each point around the Earth up to thousands of km? Is there a formula? Or do I need to download a vector field from...
  33. Creedence

    I Equilibrium state of sourceless EM field

    Given a box made of perfectly conducting material. At some part of it at t=0 there is a localized magnetic field. It's sourceless and there aren't any dissipation. After t=0 it starts to spread and fill the box. What is the equilibrium state? Thanks for the answer(s), Robert
  34. bland

    I Spacetime Geodesics at Sea Level & Zoomed Out

    I suppose that that a spacetime geodesic of an object falling on Earth would a appear as straight line. But what I'd like to see is a whole bunch of relevant geodesics that would represent falling bodies all around the Earth such that one could zoom out and so see these straight line geodesics...
  35. G

    A Correlation function of a Klein-Gordon field

    First, let me introduce the notation; given a Hamiltonian ##H## and a momentum operator ##\vec{P}##, and writing ##P=(H,\vec{P})##. Let ##|\Omega\rangle## be the ground state of ##H##, ##|\lambda_\vec{0}\rangle## an eigenstate of ##H## with momentum 0, i.e. ##\vec{P}|\lambda_\vec{0}\rangle=0##...
  36. 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...
  37. Cyclone Charlie

    Particle in a magnetic field -- question

    I went with R=mv/qb, thus -> 6.64e-27*35.6e3/2*1.6e-19*1.8, and got 4.1e-4 m (metres), so diameter is 2R, 8.2e-4 m, as an answer, the reference site gives 3.95e+10 m as the answer, who's right here?
  38. N

    Programs Which field of study teaches how to make electronic components

    Hello everyone, I was wondering which field of study teaches how to make electronic components. For example, I would like to learn how to make resistors, caps, led, transistors... I have more or less of the theory, such as what the Dirac gaps are, if we talk about semiconductor... But what I...
  39. G

    Relativistic charged particle in a constant, uniform EM field

    I have to find pμ(τ) of a particle of mass m and charge q with v(0) = (vx(0), vy(0), vz(0)) in a electric field E parallel to the y-axis and a magnetic field B parallel to z axis, both constant and uniform, with E = B. Here follows what I have done (see pictures below): I wrote 4 differential...
  40. A

    Guiding Magnetic Fields in Solenoid Coils: Design and Material Considerations

    Hi, at this moment I'm trying to figure out one thing. I have a solenoid with a core that has an empty middle, the flux normally loops back around the outside of the solenoid to the other side where it enters back into the core. I need to route this field between the two ends of the solenoid...
  41. navneet9431

    Would electric field exist if there were only one type of charge?

    I believe the answer is incorrect, reasons: The answer assumes that electric field will exist . But this is not the case , until and unless there is a bipolarity there cannot be an electric field ( in case of isolated charged objects, the field exists because the bipolarity is separated by a...
  42. K

    I Boundary terms for field operators

    Hello! In several of the derivations I read so far in my QFT books (M. Schawarz, Peskin and Schroeder) they use the fact that "we can safely assume that the fields die off at ##x=\pm \infty##" in order to drop boundary terms. I am not sure I understand this statement in terms of QFT. A field in...
  43. Zahid Iftikhar

    Electric Field of a moving charge

    When a charge is at rest, it has an electric field only. When the charge starts moving , it is said to have accompanied a magnetic field. My question relates to its electric field while in motion. Does it still exist or not? I know in electron guns electrons are deflected while passing thru the...
  44. E

    Working out the kinetic energy of a body due to a gravitational field

    Usually when setting up an energy equation I use the general form, (Initial KE) + (Initial PE) + (Any other work done to the body) = (Final KE) + (Final PE) ... For this I said the initial GPE and KE are 0, and the work done by the field is GMm/x (derived by integrating a force of -GMm/r^2 from...
  45. D

    I E- & Ions Deflection by Earth's Magnetic Field

    Do solar wind electrons turn left and positively charged ions turn right if they are interacting weakly due to long distance with Earth's magnetic field and fail to complete a loop for the electrons that are on the left of Earth and ions on the right? I assume electrons on the right and ions on...
  46. Noelani2306

    Electrical field outside a hollow spherical conductor

    Hello everyone, There is an electrical field inside and outside (at the same time) the spherical hollow conductor when we place positive or negative charge inside, isn't it? I know this is because of the induced charges on the inner and outer surfaces of the conductor. There is no field inside...
  47. J

    Electric Field for Charge Distributions

    We are given: q1 = +2.0 x 10-5 C, q2 = q3 = -3.0 x 10-5 C, r31 = r21 = 2 m a) We start by finding the electric force between q3 to q1 and q2 to q1 FE31 = k * q1 * q3 / r312 FE31 = (9.0 x 109 Nm2/C2) * (+2.0 x 10-5 C) * (3.0 x 10-5 C) / (2 m)2 FE31 = 1.35 N FE21 = k * q1 * q2 / r212 Since...
  48. P

    Calculating a Non-Uniform Electric Field Given 6 different Electrode Pairs

    I know how to find the electric field of more traditional designs i.e. a sphere, through Gauss' Law but I don't think Gauss' Law applies to this scenario. I tried to separate each part of the electrode into simple spheres and rods and using Gauss' Law to find these individual elements. This...
  49. Moara

    Eletromagnetism: Copper Plate on a Spring Oscillating in a Magnetic Field

    Tried to find the resultant force, but I can't see how the magnetic field affects. I used Faraday's law to find the the diferece of potentials in the plate Wich should be B.d.v, where v is the vertical velocity of plate, but there were not given the resistance or resistivity to relate with the...
  50. J

    Moving Electrons in a Uniform Magnetic Field

    a) We can solve for acceleration by looking at FNETy FNETy = FE (G is negligible) FNETy = m * a The mass (m) of an electron is 9.1093836 x 10-31 kg. The elementary charge (q) of an electron is -1.60217662 x 10-19 C a = ε * q / m a = (4.0 x 102 N/C * 1.6022 x 10-19 C) / 9.1094 x...
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