Magnetic dipole Definition and 125 Threads

A magnetic dipole is the limit of either a closed loop of electric current or a pair of poles as the size of the source is reduced to zero while keeping the magnetic moment constant. It is a magnetic analogue of the electric dipole, but the analogy is not perfect. In particular, a true magnetic monopole, the magnetic analogue of an electric charge, has never been observed in nature. However, magnetic monopole quasiparticles have been observed as emergent properties of certain condensed matter systems. Moreover, one form of magnetic dipole moment is associated with a fundamental quantum property—the spin of elementary particles.
The magnetic field around any magnetic source looks increasingly like the field of a magnetic dipole as the distance from the source increases.

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  1. J

    Forces and fields: magnetic dipole vs electric monopole

    Two electrons, they have their electric fields and magnetic dipole moments. Their electric field is proportional to 1/r^2, and electric force is also proportional to 1/r^2. http://en.wikipedia.org/wiki/Magnetic_dipole%E2%80%93dipole_interaction However, their magnetic dipole field is...
  2. I

    Calculating change in Magnetic Dipole Moment

    In one moment in time you have a charge going about in a circle of radius r. in another moment in time the charge goes in the same circle but faster, where Δv is the difference in speed. i want to find the change in the magnetic dipole moment Δm.if magnetic dipole moment m=IA (assuming uniform...
  3. ShayanJ

    Charged particle on a sphere with magnetic dipole at its center

    I just wanted something to play with so I thought of this problem and solved it but now I have questions about it. Consider a charged particle with charge q and mass \mu which is constrained to move on the surface of a sphere of radius R. There is a magnetic dipole with moment \vec m=m \hat z...
  4. C

    Free electrons and intrinsic spin magnetic dipole moment orientation?

    Are there any experiments or theories about the relation between magnetic dipole moment orientation and velocity vector of free electrons?
  5. majormaaz

    Earth's Magnetic Dipole Moment

    Homework Statement The Earth's magnetic dipole moment is 8.0 x 1022 A m2. (a) What is the magnetic field strength on the surface of the Earth at the Earth's north magnetic pole? You can assume that the current loop is deep inside the earth. 6.17e-5 T (b)How does this compare to 5.0 x...
  6. ShayanJ

    Calculate Magnetic Field of Moving Magnetic Dipole

    Does anyone know how to calculate the magnetic field or flux of a uniformly moving magnetic dipole with magnetic dipole moment \vec{M} pointing along the direction of motion? Thanks
  7. V

    Direction of a moving charage and energy state of a magnetic dipole?

    Homework Statement 1. A wire of length L and carrying current I is bent into a square loop to form a magnetic dipole. This dipole is then oriented in a uniform magnetic field of magnitude B such that the dipole is in its lowest energy state. What is the value of the dipole's energy with this...
  8. V

    Energy of a magnetic dipole moment

    Homework Statement The z component of the magnetic dipole moment due to the spin of an electron about its axis is μz = +/- eh/4∏m, where h = 6.63 x 10-34 J s is Planck's constant. A) If μz is parallel to a magnetic field of 10 T, how much energy in electron volts must be supplied to reverse...
  9. B

    What is the difference between magnetic dipole moment and torque ?

    imagine a door shaped circuit in the between a south and north pole such that the long sides are perpendicular to the magnetic field created by the magnet , now in my physics book , it says that the torque that rotates the door is equal to B * Md where Md is the magnetic dipole moment which...
  10. PhizKid

    How to find magnetic dipole force?

    Homework Statement The relationship of dipole force and distance is noted by F ∝ ##d^{-3}##. One magnet is placed on a weighing scale and set the mass is set to equilibrium. Another magnet, with its positive end pointing down, is lowered from directly above towards the positive end of the...
  11. O

    How do scientists know the direction of Magnetic dipole moment?

    How they know, how to see the spin of electron>?? Without external field applied, there is random dipole in the paramagnet. for diamagnet, without external field , there will be no dipole exist. Thanks.
  12. O

    Closed integral problem: field in the plane of a magnetic dipole

    I have read about Biot-Savarts law but I have no idea how to solve it when the curve is dependent of some variable. My books in mathematics don't help, nor my books in physics. You are welcome to give me a link where I can read about this, but first let me know if I have got it right this far...
  13. P

    How to calculate the magnetic dipole moment?

    How to calculate the magnetic dipole moment?? Does anyone out there know how I can calculate the magnetic dipole moment of a simple bar magnet? Or any kind of magnet? Without using this formula: \tau = μ x B
  14. U

    What is the force on a magnetic dipole in a coil at r = 0?

    Homework Statement Homework Equations The Attempt at a Solution I found dB/dr to be constant near r = 0, so it's a straight line, implying B increases linearly with r near r = 0. For the second part, I assume the setup is as such, if not placing the dipole with its axis parallel to the coil...
  15. M

    Einstein summation notation for magnetic dipole field

    I can do this derivation the old fashioned way, but am having trouble doing it with einstein summation notation. Since \vec{B}=\nabla \times \vec{a} \vec{B}=\mu_{0}/4\pi (\nabla \times (m \times r)r^{-3})) 4\pi \vec{B}/\mu_{0}=\epsilon_{ijk} \nabla_{j}(\epsilon_{klm} m_{l} r_{m} r^{-3})...
  16. U

    Magnetic Field of a Magnetic Dipole

    Homework Statement I'm not sure how they got the components of the B-field in the r and θ direction. I know the B-field along the ∅ direction is zero though. The Attempt at a Solution Here I have found the B-field at points P, Q and S that are very far along the z, x and y axis...
  17. D

    Simulating Angular Momentum and Torque in Particle Interactions

    I am simulating protons and electrons in a simulator that runs 1 femto seconds per second up to 1 second per second. So it can accurately show the passage of charge particles through space with data being updated on their displacement, velocity and acceleration. However I am now adding in...
  18. facenian

    Magnetic dipole moment energy question

    Hello, I have this problem. I calculated the dipole energy of a dipole moment in an external field using the equation U_m=\frac{1}{2}\int\vec{A}\vec{J}dr^3=\frac{1}{2} \vec{\mu}.\vec{B} however when the force on a dipole is calculated using \int\vec{J}\times\vec{B}dr^3 the formula...
  19. T

    Modeling Magnetic Dipole Interaction Between Permanent Magnets

    Two permanent magnets are on the table some distance apart and having some arbitrary orientation relative to each other. When we let go of them they will rotate and translate until they stick together. I am looking for suitable equations to model this interaction on a computer. Also, if anyone...
  20. N

    Magnetic dipole in magnetic field

    Hi The energy U of a magnetic dipole in an external magnetic field is given by U = -\mu \cdot B so the energy is zero when they are perpendicular and maximal when they are antiparallel. This makes very good sense intuitively. Quantum-mechanically we have that \mu = -m_Fg_F \mu_B...
  21. J

    Magnetic Dipole Moment of an Electron

    Homework Statement I am so stuck on this, and would be very thankful for any help! a). Calculate the magnetic dipole moment of a single atom, based on the following model: One electron travels at speed 7.40 × 10^6 m/s in a circular orbit of diameter 2 × 10^-10 m. b). The individual atomic...
  22. N

    Proof on Magnetic Dipole in an homogeneous magnetic field

    Homework Statement A magnetic dipole of strength m is placed in an homogeneous magnetic field of strength Bo, with the dipole moment directed opposite to the field. Show that, in the combined field, there is a certain spherical surface , centered on the dipole , through which no field lines...
  23. J

    How Do You Calculate the Magnetic Moment of a Complex Wire Loop?

    Homework Statement A wire is bent into the shape shown in the figure. The semi-circular part has a radius r = 4.00 cm and the rectangular part has a width w = 1.00 cm. A current of 0.300 A runs through the loop. What is the magnitude of the magnetic moment of the loop? Note: The figure...
  24. R

    Larmor Precession and Force on a Magnetic Dipole

    Homework Statement I have two questions. Both involve derivations from textbooks, not end-of-the-chapter problems. The two textbooks are Quantum Mechanics by Griffiths, and A Modern Approach to Quantum Mechanics by John Townsend. My first question is about the discussion of Larmor...
  25. L

    Can a Magnetic Dipole Form a Circle?

    Sorry for my lack of knowledge, I'm in Grade 7 I just learned that Magnets have dipoles--like this: If those dipoles formed a circle, wouldn't it be possible to create perpetual motion?
  26. H

    Magnetic torque acts about which point on magnetic dipole?

    1. when there is a current in a loop and it is placed in a magnetic field then there will be the torque on it along the direction of mxB axis.but that axis will pass through which point.will that torque act through the center of the loop only?? 2. suppose a current (I) carrying loop (of R)is...
  27. C

    What is the average magnetic dipole moment?

    Though this might be absurd, I would seriously like to know the average magnetic dipole of a magnet. For example, you might consider a regular magnet in a remote control car's motors, or any other suggestions too. And I have one more doubt- I know that e.m.f=-d(phi)/dt and phi=integral(B.dS)...
  28. O

    Einstein-de Haas Experiment: Magnetic Dipole Moment Alignment

    Hi. So, you surround a ferromagnet with a solenoid. Run current through solenoid to create B field withing. 2 Questions: 1:Why do the magnetic dipole moments in the ferromagnet "align" with the magnetic field of the solenoid? Doesn't lenz's law say that the magnetic field within the...
  29. A

    Magnetic dipole moment of a ferromagnetic cylinder

    I have a Nickel cylinder, 5 micron in diameter and 10 micron in length. I know the external field \vec{B} is 80 gauss, what is the formula for the magnetic dipole moment of this cylinder in the field? Now I only have the formula for magnetic dipole of spheres, which is \mu = \frac{4}{3}\pi...
  30. Q

    Magnetic dipole in two reference frames (special relativity problem)

    Homework Statement An EM wave traveling in vacuum has a magnetic field in the lab frame K which is given by \vec{B}(\vec{x},t) = \hat{z} B0 \cos{kx-\omega t} where Bo, k are positive constants and omega = ck. a) A point magnetic dipole, m, where m = \hat{y}m0 (m0 constant) is at rest in...
  31. B

    How Does Spin Angular Momentum Influence Magnetic Dipole Energy in a Field?

    Homework Statement A molecule possessing a magnetic dipole moment has squared spin angular momentum 3/4 h bar. give an expression for the energy of the molecule when it is stationary in a magnetic field of flux density B. Write down the partition function Z. Homework Equations...
  32. W

    Direction of electron's total magnetic dipole moment

    Hi, What direction does the electron's total magnetic dipole moment point relative to it's total angular momentum vector L+S? It seems to me that it would point oppositely to J=L+S since the spin magnetic dipole moment and the orbital magnetic dipole moment are both opposite to L and S, but...
  33. A

    Explain how an atom may have a permanent magnetic dipole moment

    Explain how an atom may have a permanent magnetic dipole moment? Many thanks...
  34. A

    <\psi_b | z \dot{x} | \psi_a> (magnetic dipole & quadrupole transitions)

    This is part 2 of problem 4.8 from "Physics of Atoms and Molecules - Bransden, Joachain" Homework Statement Deduce [4.106] from [4.105] Homework Equations \tilde{M}_{ba} = - \frac{m\omega_{ba}}{\hbar c} \langle \psi _b \vert z \dot{x} \vert \psi _a \rangle [4.105]...
  35. R

    Charge and current distribution for magnetic dipole in motion

    Homework Statement Find rho(r,t) and j(r,t) for the following: a) point charge q in uniform motion b) electric dipole p in uniform motion c) magnetic dipole m in uniform motion Homework Equations j(r,t) = v rho(r,t), so if we know rho, we know j The Attempt at a Solution a)...
  36. Y

    Help in TEM wave propagation for a solenoid or magnetic dipole.

    I am trying to figure out how the TEM wave looks like and how it propagate outward. Attached is a pdf of a drawing with only the solenoid and show the winding that the current is flowing in CCW and a reference. Also I draw a loop with one resistor and show the induced current and the polarity of...
  37. D

    Magnetic dipole above a superconductor.

    Homework Statement Consider a magnet floating over a large piece of superconductor. Treat the magnet as a perfect dipole m floating a distance h from the surface of the superconductor, which we take to be the x–y plane. The dipole is oriented at an angle of θ to the z-axis, and without loss...
  38. G

    Electric & magnetic dipole moment

    Hello, I have doubts with this problem, I'm not sure, if my solutión is right, so, here we go Let's two equal charges with the same charge but opposite signs, positive and negative, in a circle, such a distance between them is constant and equal to diametre of the circle. Both charges, turn...
  39. C

    Do Gluon's have a magnetic dipole moment ?

    Do Gluon's have a magnetic dipole moment ? I hope this is the right place to post this.
  40. N

    Elementary confusion about the magnetic dipole moment and field lines

    simple magnetic dipole moment with impossible field lines? clueless. Hello, I'm taking a first year university course in electromagnetism. At a certain point we came upon the torque on a current loop in a uniform magnetic field. There we introduced the magnetic dipole moment \overline{\mu} =...
  41. K

    Energy of a magnetic dipole in an external B field

    As in Feynman's lecture on physics vol 2, he showed that the "true energy" of a magnetic dipole(current loop) in an external B field is m*B, not -m*B. Basically the argument is if you want to pull a current loop from infinity to the final position, you must do extra work to keep the current in...
  42. L

    Calculating Magnetic Dipole Moment & Torque of Coil in Magnetic Field

    Homework Statement A circular coil having 20 turns and a radius of R = 12.8 cm carries a current of 2.70 A. It is placed in a uniform magnetic field of 60.0 mT. The initial angle between the magnetic moment of the coil μ and the magnetic field B is 26.0o. 1)Calculate the magnetic dipole...
  43. R

    Calculating Magnetic Dipole Moment of Spin-2 Point Particle with Proton Mass

    Homework Statement ..Is it possible to find the Magnetic Dipole Moment of a point particle with spin quantum number 2 and mass equal to that of a proton. I'm not sure how to start this question as there's nothing on it in the textbooks I have! Thanks
  44. M

    Find Integrals of Motion for Particle in Magnetic Dipole Field

    Find the fi rst integrals of motion for a particle of mass m and charge q in a magnetic field given by the vector potential (scalar potential \Phi= 0) (i) of a constant magnetic dipole m_{d} A=\frac{\mu_{0}}{4 pi}\frac{m_{d} \times r}{r^{3}} Hint: Cylindrical coordinates are useful...
  45. D

    Understanding Magnetic Dipole Moments: A Beginner's Guide

    i want to learn about magnetic dipole moments but don't have a good grasp on it
  46. D

    Change in orbital magnetic dipole moment of the electron due to unifrom B field

    Homework Statement Assume that an electron of mass m and charge magnitude e moves in a circular orbit of radius r about a nucleus. A uniform magnetic field B is then established perpendicular to the plane of the orbit. Assuming also that the radius of the orbit does not change and that the...
  47. D

    Force on point magnetic dipole

    Hi guys, I'm involved in a research project regarding discrete bit patterned media and I was tasked to figure out how a magnetic force microscope works for imaging magnetic islands on thin magnetic films coated on silicon substrate, as part of a preparatory literature review. So I pulled out...
  48. Matterwave

    Solving E&M Midterm: Force & Torque on Magnetic Dipole

    So I got a question on a E&M Midterm: There is a line current of I at the origin going in the Z direction. There is a magnetic dipole of: \vec{m}=m_r\hat{r}+m_\varphi\hat{\varphi} located at (r,\varphi). What is the force and torque on this magnetic dipole? So I used the equations...
  49. J

    Magnetic Dipole Moment of a Coil

    Homework Statement You have a coil of N turns, with current I through it. It is in a magnetic field B, which causes it to feel a torque. Give an expression for its magnetic dipole moment. Homework Equations The Attempt at a Solution Well, I know magnetic dipole moment is A...
  50. R

    Potential Energy for magnetic dipole

    I am not understanding why the potential energy (U) for a magnetic dipole is at it's maximum when the magnetic dipole moment is antiparallel to the magnetic field (B), why U is at it's minimum when the magnetic dipole moment and B are parallel, and why U is zero when B and the magnetic dipole...
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