electromagetism

  1. R

    I 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=...
  2. dude2

    A Aharonov - Bohm effect exercise

    Does anyone know the answers to this, or can hopefully guide me to a text that will help me solve this aharonov-bohm problem? Here is the given: Particles (of mass m, and charge q), are driven through two slits that have distance d between them, in a screen that is far away (L>>d) from the...
  3. N

    How to transmit a signal (530 - 550 Khz) to a point

    Hi everyone, I'm pretty new to electromagnetism and have no experiences in this topic. I have a signal generator (Digital Dual Channel Funktion Signal Generator) and want to generate two signals (530 and 550 Khz signal) and want to transmit these generated signals to the points on a table...
  4. C

    What will the phasor diagram of this LCR circuit looks like?

    I know the current of capacitor and inductor must be parallel but pointing in opposite direction due to the fact they are connected in parallel thus having same voltage (please see attached screenshots). The current of resistor will simply be the sum of these two vectors, but what about its...
  5. S

    I Consistent Treatment of Forces

    Under Newton, gravity is what I term an "invisible magic rope" that pulls you down. Enter Einstein. We do away with the invisible magic rope, and say that space (or space-time) is warped by mass. However, we still have other forces, that (as far as I know, anyway) are "invisible magic ropes."...
  6. Beelzedad

    I Why am I getting Maxwell's second equation wrong?

    While going through an article titled "Reflections in Maxwell's treatise" a misunderstanding popped out at page 227 and 228. Consider the following equations ##(23\ a)## and ##(23\ c)## in the article (avoiding the surface integral): ##\displaystyle \psi_m (\mathbf{r})=-\dfrac{1}{4 \pi} \int_V...
  7. W

    Derivation of the wave equation on a curved space-time

    I'm confused by this question, from minimal coupling shouldn't the answer simply be ## \nabla^a \nabla_a F_{bc} = 0 ##? Any help would be appreciated. EDIT: I should also point out ##F_{ab}## is the EM tensor.
  8. lord_sphinx

    Determining D, H, and β

    In a certain region for which σ=0, μ=2μ0, and ε=10ε0, J= 60sin(109t - βz). Determine D, H, and β.
  9. Hawkingo

    I Can this event vary relatively?

    Suppose we take a charged particle and a magnet and place them at some particular distance apart .Now let's take 2 frame of reference. [the charged particle and the magnet are in rest with respect to each other through out the whole event]{both of the frames are inertial} frame(a): this frame...
  10. J

    I Destructive interference in Unpolarised light

    Destructive interference is excellently demonstrated in Young's double slit experiment, where dark regions are formed due the waves being out of phase. However, what really confuses me is that unpolarised light has intensity. Assuming we had perfectly unpolarised light, as in where the...
  11. Klaus von Faust

    Interesting Magnetic Field Induction Problem

    1. Homework Statement Suppose we have an isolated, long, narrow straight wire with low electrical resistivity. A constant current ##I## is sent through this wire. We know that if an electron is sent on a path which is perpendicular to the wire, towards it, with an initial speed ##v_0##, and the...
  12. astroman707

    Charged pendulum problem

    1. Homework Statement A cork ball is suspended at an angle from the vertical of a fixed cork ball below. The mass of the suspended ball is 1.5x10^-4 kg. The length of the suspension thread is .1m. The fixed ball is located .1m directly below the point of suspension of the suspended ball. Assume...
  13. Burhan Uddin

    Calculating the work done using a line integral

    1. Homework Statement a) A point charge + q is placed at the origin. By explicitly calculating the relevant line integral, determine how much external work must be done to bring another point charge + q from infinity to the point r2= aŷ ? Consider the difference between external work and...
  14. iVenky

    I From Maxwell's equations to EM waves

    Hi, I just finished studying Maxwell's equations. Based on my understanding, when you solve maxwell's equation, you get the wave equation and it simplies to in a charge and current-free region. I understand that these two equations are similar to an equation of a wave in space. What I am...
  15. ZuperPosition

    A Abstract definition of electromagnetic fields on manifolds

    Hello, In the sources I have looked into (textbooks and articles on differential geometry), I have not found any abstract definition of the electromagnetic fields. It seems that at most the electric field is defined as $$\bf{E}(t,\bf{x}) = \frac{1}{4\pi \epsilon_0} \int \rho(t,\bf{x}')...
  16. A

    I Electromagnetic braking

    I'm working on a project and came across electromagnetic braking recently and I'm really curious to know if it's really feasible. The project in brief is a vehicle on a monorail at speeds of +600km/hr needs to be stopped. The monorail is made of an alloy of aluminium. I have no background in...
  17. B

    I Meaning of "aligned" magnetic dipole

    Just for the record, The text is Introduction to Electrodynamics (4th Edition) by David J. Griffiths Chap.6. What does "when the magnetic dipoles are aligned" mean? Does it mean Both moments are parallel to each other's magnetic field? i.e. ##m\times B = 0## for both? Or is it ##m_1\parallel...
  18. B

    I The integral form of Gauss' theorem

    In many texts I have seen, Gauss theorem has the form of$$\frac{q}{\epsilon_0}=\oint\vec{E}d\vec{A}$$ Why a line integral symbol was used for this surface integral everywhere? The more I see it the more I believe there is something wrong with my understanding about this. I didn't think too much...
  19. P

    I Are these instances of identical magnetic fields?

    Are both magnetic fields emanated from an electromagnet fed with a current spike from a charge capacitor and a rotating static magnetic feild from permanent magnets instances of time varying fields? The permanent magnet would be attached to perhaps some rotating disc thus passing over a target...
  20. archaic

    Force of one distribution of charge on another

    1. Homework Statement I need help on solving this exercise : We have a ring of radius = ##a## uniformly charged (total charge = ##Q##) and on its axis a segment ##OA## (length = ##a## also) of uniformly distributed positive electric charges with the charge density ##\lambda'## and of total...
  21. A

    I What was the value of the permeability constant in 1865?

    What is the value of the permeability constant in 1865, the time when Maxwell's theory was first published? What was the experimental method used to determine the constant. Who did the experiment.
  22. Jefffff

    Charging a battery by moving a magnet randomly in 2D plane?

    I'm sorry if this question is a little abstract, but would appreciate any guidance! It's for a DIY project I am considering. Suppose you have a flat panel mounted on a wall, and a very strong magnet that will move in any direction on the plane of the flat panel. Through any possible arrangement...
  23. It's me

    Show that the radiation field is transverse

    1. Homework Statement Show that the radiation field is transverse, ##\vec{\nabla}\cdot\vec{A}=0## and obeys the wave equation ##\nabla^2\vec{A}-\frac{1}{c^2}\partial_t^2\vec{A}=0##. You should start from the expansion of the quantum Electromagnetic field. 2. Homework Equations...
  24. B

    Propagation of EM waves

    1. Homework Statement Use Maxwell's equations to elaborate an coherent explication of why electromagnetic waves propagate independently of the source that produces them. 2. Homework Equations Maxwell's equations in vacuum: ##\nabla * E=0## ##\nabla * B=0## ##\nabla \times E =...
  25. T

    Toroid with Air Gap magnetostatics problem

    1. Homework Statement consider a toroidal electromagnet with an iron ring threaded through the turns of wire. The ring is not complete and has a narrow parallel-sided air gap of thickness d. The iron has a constant magnetization of magnitude M in the azimuthal direction. Use Ampere's law in...
  26. mheruian

    Winding Direction Consideration (Proper Winding)

    Hello, I'm boy who suddenly been strucked by curiosity on how hand crank generator works and i watch and read some of how to create one, specially this one on youtube: and i want to create one but i don't have a 3D printer, but i saw some alternative but as i do/design my own coil based on...
  27. Clay

    I Inverse square law confusion

    i have heard how our broadcasts will be seen by aliens far away or whatever. but i realize those signals are going to "attenuate" by d^-2 anyway... how come in astronomy we can see light sources millions of light years away? shouldn't those signals be far too weak to detect after such a long...
  28. A

    Is today's exam question unsolvable? - Proton Motion in a Magnetic Field

    <Moderator's note: Moved from a technical forum and thus no template.> Hello all, Earlier today I had an electromagnetism exam, and it seems to me that this problem is unsolvable. There's just too little information given. A proton enters an uniform magnetic field. It's initial speed v is...
  29. P

    Courses Review Griffiths E/M before Jackson?

    Hello, I will be starting my junior year this August, I shall be having the dreaded advanced electromagnetism course that follows Jackson's book the coming semester. Unfortunately, I didn't work very hard during my freshman year e/m course (which uses Griffiths' book) and have a few gaps in my...
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