What is Magnetic dipole moment: Definition and 59 Discussions

The magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include: loops of electric current (such as electromagnets), permanent magnets, elementary particles (such as electrons), various molecules, and many astronomical objects (such as many planets, some moons, stars, etc).
More precisely, the term magnetic moment normally refers to a system's magnetic dipole moment, the component of the magnetic moment that can be represented by an equivalent magnetic dipole: a magnetic north and south pole separated by a very small distance. The magnetic dipole component is sufficient for small enough magnets or for large enough distances. Higher-order terms (such as the magnetic quadrupole moment) may be needed in addition to the dipole moment for extended objects.
The magnetic dipole moment of an object is readily defined in terms of the torque that object experiences in a given magnetic field. The same applied magnetic field creates larger torques on objects with larger magnetic moments. The strength (and direction) of this torque depends not only on the magnitude of the magnetic moment but also on its orientation relative to the direction of the magnetic field. The magnetic moment may be considered, therefore, to be a vector. The direction of the magnetic moment points from the south to north pole of the magnet (inside the magnet).
The magnetic field of a magnetic dipole is proportional to its magnetic dipole moment. The dipole component of an object's magnetic field is symmetric about the direction of its magnetic dipole moment, and decreases as the inverse cube of the distance from the object.

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  1. S

    Magnetic Dipole Moment - Vector Orientation

    Guys, I don't quite understand the concept of magnetic dipole moment as a vector. Suppose we have a magnet (like a rod) in 3 dimensional space. North pole at (0, 0, 0) and South pole at (0, 1, 0). How would the magnetic dipole vector \vec{m} be oriented? Thanks.
  2. E

    Calculating Magnetic Dipole Moment of a Sphere

    [SOLVED] Griffiths 5.58 Homework Statement A uniformly charged solid sphere of radius R carries a total charge Q, and is set spinning with angular velocity \omega. What is the magnetic dipole moment of the sphere.Homework Equations The Attempt at a Solution The magnetic dipole moment of a...
  3. M

    Magnetic Dipole Moment and Angular momentum

    Homework Statement Show that the magnetic dipole moment M of an electron orbiting a proton nucleus of a hydrogen atom is related to the orbital angular momentum M=(e/2m)L Homework Equations M=NIA, Torque =MB, F=qvB=v^2/r, L=Iw=mrv=rp (where p=mv) N=1 in this case I assume? The...
  4. S

    What is the magnetic dipole moment of the sphere?

    Homework Statement A uniformly charged solid sphere of radius R carries a total charge Q, and is set spinning with angular velocity \omega about the z axis. (a) What is the magnetic dipole moment of the sphere? Homework Equations \vec{m} = I \int d\vec{a} The Attempt at a...
  5. S

    Magnetic dipole moment of a sphere

    Homework Statement Find the magnetic dipole moment of a spherical shell of radiu R carrying a uniform surface charge sigma, set spinning at angular velocity omega. Homework Equations \vec{m} = \frac{1}{2} \int_{S} \vec{r'} \times \vec{K} (\vec{r'}) da' The Attempt at a Solution So...
  6. S

    What is the magnetic dipole moment of a rotating charged record?

    Homework Statement A phonograph record of radius R carrying a unifrom surface charge sigma is rotating at a cosntant angular velocity omega. Find its magnetic dipole momentHomework Equations m = int I \bullet da The Attempt at a Solution Need to find the current first well the sruface charge...
  7. siddharth

    Magnetic Dipole Moment of a Surface Current Loop

    For a current loop, the magnetic dipole moment is defined as i \int d\vec{a} Now, if I'm given a surface current 'K', how can I find the magnetic dipole moment? For example, if a disc of surface charge [itex] \sigma [/tex] is rotating with angular velocity [itex] \omega [/tex], what is it's...
  8. T

    Magnetic dipole moment homework

    Hello, i have absolutely no clue on how to start this one: a sphere of radius R has a uniform volume charge density \rho. Determine the magnetic dipole moment of the sphere when it rotates as a rigid body with angular velocity \omega about an axis through its center. thanks for the help...
  9. H_man

    Magnetic Dipole Moment does not include the permeability of free space?

    Magnetic Dipole Moment does not include the permeability of free space? Hi, The formula for a magnetic field in a current loop involves the permeability of free space. But the formula for the magnetic dipole moment which seems to represent the flux through a current loop does not...
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