Magnetic dipole in an external magnetic field

In summary, The conversation discusses a diagram of a magnetic dipole being affected by an external field and a magnetic field. There is confusion about the direction of deflection and the use of the right hand rule to determine the force and direction of movement. The dipole also has angular momentum and will precess, but the "motor rule" is cited as the reason for the deflection to +y.
  • #1
rndnrg
3
0
I've run across a diagram that really is driving me crazy. The torque on a mag. dipole should be simply be τ = m X B, where B is the external field as usual.

In the image I've attached, there is a large external field, not shown, in the direction of Z which is holding the dipole in the +Z direction. We then switch on a mag. field in the +X direction. What's shown is the dipole moving towards +Y... :bugeye:

I would expect it to be deflected down towards +X. Am I right in thinking that the torque vector really shouldn't be the direction of movement. Rather, you should use the right hand rule to determine the force and direction of movement. If I'm completely wrong let me know. I've been staring at this for days now. :)
 

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  • #2
Actually I should have placed this thread in classical physics. To late now :(
 
  • #3
The picture is hard to read. My guess is that the dipole also has angular momentum and will precess like a gyroscope.
 
  • #4
It does have angular momentum, but how would that cause a deflection to +y? From the "NMR techniques" at the top you probably already know that precession is going on... but we're in a rotating fram of reference. We're treating everything as static.

To add more information:
The picture doesn't capture it, but in the text just following the diagram the author cites the "motor rule" for this deflection to +y.

The motor rule(left hand): (field)X(current). However we're talking about two magnetic fields. If you do a quick thought experiment about the effect of a current loop producing a dipole and how it would be affected by being immersed in a field you should still come to the conclusion that it would deflect to +x.
 
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1. What is a magnetic dipole?

A magnetic dipole is a physical system that consists of a pair of opposite poles, such as a north and south pole, that create a magnetic field. This magnetic field is strongest at the poles and decreases in strength as you move away from the poles.

2. What is an external magnetic field?

An external magnetic field is a magnetic field that is created by a source outside of the system or object being studied. This external field can interact with the magnetic dipole and cause it to experience a force or torque.

3. How does a magnetic dipole behave in an external magnetic field?

In an external magnetic field, a magnetic dipole will align itself with the direction of the magnetic field lines. If the external field is strong enough, the dipole may be forced to rotate to align itself with the field. This behavior is known as magnetic dipole moment.

4. What is the significance of understanding magnetic dipole behavior in an external magnetic field?

Understanding how a magnetic dipole behaves in an external magnetic field is important in many areas of science and engineering. It can help us understand the behavior of materials in magnetic fields, as well as how to manipulate and control magnetic fields for various applications.

5. How is magnetic dipole moment calculated?

Magnetic dipole moment is calculated by multiplying the strength of one of the poles by the distance between the two poles. It is usually represented by the symbol μ and its unit is ampere-meter squared (A m²). It is a vector quantity, meaning it has both magnitude and direction.

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