What is Magnetic dipole: Definition and 125 Discussions

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. Z

    Calculation of torque and force on magnetic dipole near infinite wire

    Please see the image further below for the definition of the coordinate system. The magnetic dipole moment of the loop is $$\vec{\mu}=\mu\hat{k}\tag{1}$$ The magnetic field for an infinite wire depends only on the distance from the wire. For the specific configuration above, we have...
  2. doomer

    I Geometry of Magnetic field lines as they approach a magnet pole?

    Magnetic field lines are loops, so at the surface of a magnet (axially magnetized) cylinder) pole they look like this? there is a dead zone at the center where there is no lines/magnetic field present? or perhaps they look more like this? lines converge in the middle to a single line or point...
  3. K

    A Phase difference between electric and magnetic dipole moment

    Hello! This question is in relation to parity violation (PV) measurements using the optical rotation technique (I can give more details/references about that, but most of it is not relevant for my question). Basically, in a simplified model, they have 2 levels (say of positive parity), g and...
  4. K

    Calculate magnetic dipole of other planets relative to the Earth

    So I have a few questions regarding the above task. I will use this equation to get the results for the different planets: Questions: So in the equation density p= mass of proton x proton density of the solar wind x 1000 000 (conversion between kgcm^-3 to kgm^-3) x 1/r^2 (I assume that I...
  5. okaythanksbud

    I Does Larmor precession change the force exerted on a magnetic dipole?

    If we have a spinning spherical charge in a nonuniform magnet field that points in one direction (for simplicity lets say B=<0,0,k*z>). Since the magnetic field is nonuniform, there will be a force exerted on the dipole, F=(mu•∇)B=mu_z*k. So in this case we expect it to be constant. This is...
  6. H

    Why a particle with spin=0 can't posses a magnetic dipole moment?

    Hi, I would like to know why a particle with spin=0 can't posses a magnetic dipole moment? Using Wigner-Eckart theorem for ##\langle j,1,m,0|j,m \rangle## I get ##\langle j'|| \vec{J}|| j \rangle = \hbar \sqrt{j(j+1)} \delta_{jj'}## It seems like the right hand side is the magnetic dipole...
  7. SR_0301

    I Question about orbital and spin magnetic dipole

    Hello guys, i want to ask you a question about orbital and spin dipole, and how this is going to influence diamagnetic or paramagnetic substances. So my question is: we know in a atom there is orbital and spin motion by electrons so possibly two magnetic dipoles. Is it correct to say that in...
  8. sergiokapone

    I How does a rotating magnet create levitation?

    Is any physical explanation of this effect?
  9. Ugnius

    Work done on a magnetic dipole (compass needle rotating)

    So this is a sketch I made of the situation and this is my approach my approach is incorrect , and Idon't seem to find the mistake , maybe B*p isn't correct. Any ideas?
  10. J

    I Magnetic dipole in vacuum near absolute zero

    Consider a single atom (or particle) in a vacuum (without electric, magnetic or gravitational field) at near zero kelvin (i.e., no photons or particles striking it). I am curious if it will still have a magnetic dipole? If there still is (which I believe), had this been shown experimentally?
  11. A

    I Orbital magnetic dipole moment of a proton

    hi every one what is the amount of orbital magnetic dipole moment of proton? this different with the intrinsic magnetic.
  12. R

    I General Magnetic Dipole Moment For an Electron in an Atom

    On the first attached page ##\mu_z## is associated with orbital angular momentum (Eq. 41.34). On the following pages (Eq. 41.38) it is associated with spin angular momentum? Are these both part of the same thing? I tried to read further but the book does not address this. In example 41.6 it...
  13. Mr_Allod

    Understanding the Force on a Magnetic Dipole in Different Orientations

    Hi there, I approached this problem by making use of the fact that a dipole can be modeled as a small current loop with the magnetic field ##\vec B_1 = \mu_0 \frac {m_1}{4\pi r^2} (2\cos \theta \hat r + \sin \theta \hat \theta)## which is the far-field approximation for a regular circular...
  14. vinamas

    Earth's magnetic dipole homework problem

    So I'm mainly having trouble with part b as I have successfully completed part a. In part b I get an answer of 6.3 x 10 ^8 Amperes which my homework tool flags as incorrect. I'm clueless as to where to go from there or why my approach is wrong?
  15. 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=...
  16. A

    Magnetic Dipole Moment of a bar magnet

    A bar magnet will have a definite magnetic dipole moment, irrespective of the presence of an external field. Why is the moment, then, always defined in relation to the torque it would feel in an external field? Is there any other definition for the same?
  17. B

    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. T

    Confusion in the derivation of the force on a magnetic dipole

    Homework Statement ok this is not a homework but i am confused by the derivation of ## f = \nabla (m . B)## both start out with ##\vec B(r) \approx \vec B_0 + (\vec r' . \nabla)\vec B|_0 ... \\ f = \iiint_{v'} \vec J( r') \times (\vec r' . \nabla)\vec B|_0 ## where prime is body coordinates and...
  19. A

    What is the size of the magnetic dipole moment?

    Consider the magnetic field B generated by a magnetic dipole. The intensity of B measured along the axis of the dipole, at a distance of 10 cm from the dipole itself, is 1.0 10-5 T. What is the size of the magnetic dipole moment? (μ0 =4π10-7 mkg/C2) a) 0.050 Am2 b) 5 10 -4 Am2 c) 0,1 Am2 d) 1 10...
  20. WeiShan Ng

    Deriving magnetic dipole moment from multipole expansion

    Homework Statement This is from Griffith's Introduction to Electrodynamics, where the book is deriving the magnetic dipole moment from multipole expansion of the vector potential The vector potential of a current loop can be written as $$\mathbf{A(r)}=\frac{\mu_0 I}{4\pi} \left[ \frac{1}{r}...
  21. peroAlex

    Induced Voltage of Rotating Circular Loop

    HI! I'm a student, this question appeared in one of the old tests. I though I had it solved but apparently I must have missed somewhere. Could someone please at least hint me where I went wrong? Homework Statement Thin wire is wound into circular frame with radius ## r = 0.05m ## which...
  22. arpon

    I Four-vector Dipole Moment: Electric & Magnetic

    What is the four-vector related to electric and magnetic dipole moment?
  23. B

    Magnetic Dipole Field from a Loop of Wire

    I am trying to understand the magnetic dipole field via loop of wire. The above pictures show how this problem is typically setup and how the field lines are typically shown. The math is messy but every textbook yields the following: β = ∇xA = (m / (4⋅π⋅R3)) ⋅ (2⋅cos(θ) r + sin(θ) θ) The...
  24. N

    Magnetic Torque on Dipole; Oscillating Magnet question

    Homework Statement A cylindrical bar magnet whose mass is 0.08 kg, diameter is 1 cm, length is 3 cm, and whose magnetic dipole moment is <5, 0, 0> A · m2 is suspended on a low-friction pivot in a region where external coils apply a magnetic field of <1.4,0,0> T You rotate the bar magnet...
  25. enerieire

    Magnetic Dipole: Discovering μ and Its Origin

    does anyone knows where this formula comes from? μ=½B(R^3) I am considering a sphere of radius R, with B its magnetic field. Who is μ? Thanks
  26. rebc

    Showing the force on a magnetic dipole

    Homework Statement We're given a situation where the circuit can move under the influence of a magnetic force. Now I need to show that the force on the magnetic dipole is Homework Equations $$\vec{F} = (\vec{m} \nabla) \vec{B} $$ The Attempt at a Solution Could I start from a given Force for...
  27. 1

    Force between 2 parallel magnetic dipole moments

    Homework Statement Find the force of attraction between 2 magnetic dipoles a distance r apart. Both dipoles point to the right. Homework EquationsThe Attempt at a Solution All I need help with is figuring out how to determine if the force is attractive or repulsive between the 2 dipole...
  28. R

    Forces acting on bar magnet inside a charged solenoid

    This is not a specific homework problem. It is a lack of understanding in theory relating to a lab report I have to write. We (my group and I) wrapped a 40 cm PVC pipe in copper wire (very densely and for almost the entire length), applied a current to it, and dropped a permanent magnet...
  29. G

    Deriving the formula for a magnetic dipole field

    Hello PF! I am trying to find out how the formula for the magnetic field of a dipole magnet is derived, so far I've delved into maxwell equations, but I am finding the math too complicated to read. My state's education system is very far behind, and I am not accustomed to characters and symbols...
  30. N

    Help with Magnetic Dipole Moment

    Im looking to find the resultant magnetic moment of a permanent magnet inside of a steel housing. Some of the remnant flux density is absorbed by the magnet and the field is altered. I want to figure out the total magnetic dipole including the presence of the steel housing. I've been using...
  31. D

    I Consistency of atomic magnetic dipole spatial orientation wi

    I've been recently trying to understand the concept of paramagnetism, but I feel like I'm running into 2 conflicting models. Stern–Gerlach seems to suggest that electron spins always point up or down to an incident magnetic field, regardless of their spatial orientation. Similarly, when...
  32. E

    What is the Significance of a Magnetic Dipole Moment?

    Is the magnetic dipole moment, the torque a material experiences when its placed in an external magnetic field? I know that the magnetic dipole moment for a current carrying wire is U=IA. The dipole moment is in the same direction of the Area, does this mean that the force it experiences will be...
  33. B

    A magnetic dipole in a magnetic field

    Let's say we have a north south bar magnet and we place it in a uniform magnetic field such that the magnetic moment is perpendicular to the magnetic field. What happens to the orientation of the magnet? In my view, the magnet receives a torque pointing out of/in to the page that causes the...
  34. D

    Finding a theoretical magnetic dipole

    I recently completed a lab over magnetism and I need some help on my results. We were asked to find the magnetic dipole moment of small neodymium magnets that were about the size of a dime and around 1/4 inch thick. I found the experimental value using my results. However, I have not been...
  35. JGBuck94

    Magnetic moment between 2 bar magnets

    Homework Statement A bar magnet floats above another bar magnet. The first has mass u1 and magnetic moment m1=m1k^ and is on the ground. The second has mass u2 and mag. moment m2=-m2k^ and is a distance z above the ground, find z 2. Homework Equations I assume I need to calculate the magnetic...
  36. K

    Magnetic dipole moment derivation

    (2) Hi. I am having a problem with understanding how to approximate 1/R in the forms of equations written above. I took this equations from a blog, and it tells that I can use talyor polynomial. but I don't get there somehow.
  37. P

    Probability that a magnetic dipole is oriented with theta

    1. the problem goes like this : The energy of interaction of a classical magnetic dipole with the magnetic field B is given by E = −μ·B. The sum over microstates becomes an integral over all directions of μ. The direction of μ in three dimensions is given by the angles θ and φ of a spherical...
  38. AwesomeTrains

    Potential of a magnetic dipole

    Hello everyone! I'm stuck at an Electrodynamics problem and would be happy for some guidance 1. Homework Statement A magnetic dipole \vec{m}(t)=\vec{m}_0cos(\omega t) at the origin can be described by the current density \vec{j}(\vec{r},t)=-\vec{m}(t)\times\vec{\nabla}\delta(\vec{r})...
  39. throneoo

    Equation of motion of magnetic dipole chain

    Homework Statement Find the equation of motion of a chain of atoms in 1D with alternating magnetic dipoles At stationary equilibrium the atoms of mass m are separated by d , all displacements are small compared to d Homework Equations U=μBx=2μ2(μ0/4π)(1/x^3) F(x)=-dU/dx The Attempt at a...
  40. phys-student

    Approximating magnetic field as the field of magnetic dipole

    Homework Statement A square wire loop of size 2a by 2a lies in the x- y plane with its center at the origin and sides parallel to the x and y axes. A counterclockwise current I runs around the loop. (a) Find the magnetic field on the z axis. [Answer: Bz = 2μ0Ia2/[(a2 + z2)(2a2 + z2)0.5]] (b)...
  41. Jimbob999

    Find magnetic dipole moment of coiled wire

    Homework Statement A 45-m long wire is coiled so that it makes a coil containing 100 circular loops, one on top of the other. If the wire carries a current of 13 A, what is the magnetic dipole moment of the coil? 21 A·m2 6.7 A·m2 3.3 A·m2 2.6 A·m2 1.2 A·m2 Homework Equations B(z) = u0/2pi...
  42. fricke

    Magnetic field due to magnetic dipole

    It is NOT a homework question. I am doing my revision and get stuck at this question. I am confused with the angle θ shown in this link: http://www.physicspages.com/2013/10/06/mutual-inductance/ Professor who wrote this solution stated that θ is the angle between unit vector z and unit vector...
  43. Luke Cohen

    Are field lines from a magnetic dipole equal in magnitude?

    http://www.physics.sjsu.edu/becker/physics51/images/28_03_Earth_magnetic_field.jpg If this is your magnetic dipole and you start at the north end and follow a field line to the south end, is the magnetic field equal in magnitude the entire way through?
  44. H

    The Earth's magnetic field is essentially that of a magnetic dipole....

    Homework Statement The Earth's magnetic field is essentially that of a magnetic dipole. If the field near the North Pole is about 10^-4 T, what will it be (approximately) 13,000 km above the surface at the North Pole? Homework Equations B = \frac{\mu _0}{2\pi}\frac{\mu}{(R^2+x^2)^{3/2}} for...
  45. T

    Magnetic Dipole less than that of the Bohr Magneton

    Hey there, The basic unit for magnetic dipoles is the bohr magneton μB = e ħ / 2 me Is it possible to have a magnetic dipole moment of a fraction of a bohr magneton, say, 0.5 μB Is it possible because the mp of a proton is greater than that of an electron, so following the same formula, its...
  46. kq6up

    Deriving the Magnetic Field from a Magnetic Dipole

    Homework Statement Show that: ##B=\frac { 1 }{ 4\pi \epsilon r^{ 3 } } \left[ 3\hat { r } \left( \hat { r } \cdot \vec { m } \right) -\vec { m } \right] ## Homework Equations B=delxA, m=a*I The Attempt at a Solution [/B] I follow my professors derivation. However, she expands the term...
  47. X

    Magnetic Dipole due to an electron's orbital motion

    Homework Statement Select all of the following which are possible combinations of Lz and θ for hydrogen atoms in a d state, where Lz is the z component of the angular momentum L, and θ is the angle between the +zaxis and the magnetic dipole moment µℓ due to the electron's orbital motion...
  48. N

    Heat capacity of magnetic dipole in magnetic field

    edit: The title is misleading, sorry. Originally I wanted to ask a question about the heat capacity but I figured it out and changed the question while forgetting to change the thread title.. Hi. OK, assume we have a classic magnetic dipole in a magnetic field with ##H= - \vec{\mu} \cdot...
  49. S

    Magnetic dipole at the centre of a sphere

    The problem is as follows: There is a point magnetic dipole embedded at the center of a sphere (radius R) of linear magnetic material of permeability μ. What is the magnetic field inside the sphere? I know that this problem has been solved in many books.But I am trying a different method. Since...
  50. A

    Moving magnetic dipole into current loop

    Homework Statement A magnetic dipole m is moved from infinitely far away to a point on the axis of a fixed, perfectly conducting (zero resistance) circular loop of radius a and self-inductance L. In its final position the dipole is oriented along the axis of the loop and is a distance z from...
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