What is the Role of Lenz's Law in Diamagnetism?

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Discussion Overview

The discussion centers around the causes and mechanisms of diamagnetism, particularly in relation to Lenz's Law and the behavior of electron pairs in magnetic fields. Participants explore theoretical explanations, implications of electron spin, and the nature of induced currents in diamagnetic materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that diamagnetism arises from paired electrons with opposite spins canceling each other's magnetic moments, but question the underlying reasons for the repulsion in an external magnetic field.
  • Others propose that the behavior of electron pairs is a fundamental property, noting that it is surprising for materials to repel rather than align with an external magnetic field.
  • One participant describes how the application of an external magnetic field increases the velocity of electrons aligned with the field, leading to the creation of a magnetic field that opposes the external one.
  • Another participant mentions the Meissner effect in superconductors as a perfect example of diamagnetism, distinguishing it from ordinary diamagnetic materials.
  • Several participants discuss the stability of electron spins and the conditions under which they might flip, referencing the Pauli exclusion principle and energy considerations.
  • One participant emphasizes that the induced electric current in diamagnetic materials is due to the orbital magnetic moment of electrons, rather than their spin, aligning with classical electrodynamics principles.
  • A later reply highlights Lenz's Law as foundational to understanding diamagnetism, explaining that the induced current opposes the external magnetic field, resulting in repulsion.

Areas of Agreement / Disagreement

Participants express a range of views on the mechanisms of diamagnetism, with no consensus reached on the explanations provided. Some agree on the role of induced currents and Lenz's Law, while others question the fundamental nature of diamagnetism and the stability of electron spins.

Contextual Notes

Discussions include various assumptions about electron behavior, the influence of atomic spacing on magnetic domains, and the implications of energy costs associated with changing electron spins. These factors remain unresolved within the conversation.

A Dhingra
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Can anyone explain what is the cause of diamagnetism...

to the extent i know is that the paired electron with opposite spin cancel out each other's magnetic moment...
is there something more to this...?

and on application of external magnetic filed why does it repel it...

thanks for any help...
 
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it appears to just be a (very surprising and odd) fundamental property of electron pairs.

ordinarily one would expect any magnet to align with not against an external field.
 
granpa said:
it appears to just be a (very surprising and odd) fundamental property of electron pairs.

ordinarily one would expect any magnet to align with not against an external field.

true it is a property ...
but there must be some explanation that it repels...

as far as i know , it is that the paired electron has net magnetic moment =0, but when an external field is supplied then the field of electron that points the same direction as the supplied one will observe an increase in its velocity and other's velocity decreases... hence magnetic field is created...

i think the magnetic field strength set up in the substance should be of good value( Bext - B elctron) ... and appears to be in the direction of the supplied field...

please tell me about it ...if u know...
 
http://en.wikipedia.org/wiki/Diamagnetism
A superconductor acts as an essentially perfect diamagnetic material when placed in a magnetic field and it excludes the field, and the flux lines avoid the region

Superconductors may be considered to be perfect diamagnets, since they expel all fields from their interior due to the Meissner effect. However this effect is not due to eddy currents, as in ordinary diamagnetic materials[/color]

I guess the effect you describe might be responsible for 'ordinary diamagnetism'.http://en.wikipedia.org/wiki/Zeeman_effect
 
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A Dhingra said:
as far as i know , it is that the paired electron has net magnetic moment =0, but when an external field is supplied then the field of electron that points the same direction as the supplied one will observe an increase in its velocity and other's velocity decreases... hence magnetic field is created...

but even if it was then why doesn't the resulting electron pair simply flip around.
It should be unstable
 
A Dhingra said:
true it is a property ...
but there must be some explanation that it repels...

I think you are just wrong about this.
Some properties are just fundamental
 
Why don't the spins alternate and thus cancel? I vaguely recall that it has to do with the spacing of the atoms. The potential energy curve there adds a factor which makes the "magnetic domain" of aligned spins energetically favorable under a narrow set of conditions.
 
granpa said:
but even if it was then why doesn't the resulting electron pair simply flip around.
It should be unstable

actually you are correct the atom should become unstable...
but it seems this does not happen , do you know why..?

i would like to discuss the cause of diamagnetism in a proper manner please.( is this way of asking for a discussion is fine) ...
 
why don't the people of science accept that if they created a term and are unable to describe it properly then it doesn't mean it cannot be described...
please , good excuse but i cannot accept it...
fundamental , but still can be questioned...
 
  • #10
JDługosz said:
Why don't the spins alternate and thus cancel? I vaguely recall that it has to do with the spacing of the atoms. The potential energy curve there adds a factor which makes the "magnetic domain" of aligned spins energetically favorable under a narrow set of conditions.

please if possible can you be more descriptive about what you are saying...
i could not understand it...
 
  • #11
Consider a helium atom. Both electrons sit in the 1 s orbital. According to the Pauli principle, they can only do so because they have different spin. To flip one spin around would necessitate lifting the electron to an electronically excited state which would cost many electron volts of energy; far more than that gained by the reduced repulsion with the magnetic field.
 
  • #12
The magnetic field induces an electric current in the diamagnetic molecules. It has nothing to do with the spin of the electrons but with the orbital magnetic moment of the electrons. The sign is the same as that of induced currents in classical electrodynamics where repulsion also occurs, see:
 
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  • #13
DrDu said:
Consider a helium atom. Both electrons sit in the 1 s orbital. According to the Pauli principle, they can only do so because they have different spin. To flip one spin around would necessitate lifting the electron to an electronically excited state which would cost many electron volts of energy; far more than that gained by the reduced repulsion with the magnetic field.

ok so considered a helium atom,with its electron moving with opposite spin, then how does application of magnetic field causes formation of opposite magnetic filed...

and as you said is it really possible to change the spin...
ya i remember , in chemistry ... we at least observe in the book... every time any compound say NaCl is formed from Na and Cl atoms ...
 
  • #14
When the atoms are brought into a magnetic field the changing magnetic field leads to an electric field (Faradays law of induction) which induces a current. As the electrons are already in their quantum mechanical ground state, this current does not decay, in contrast to the situation in classical mechanics. This current is the source of the repulsive magnetic field.
 
  • #15
hi ...
ok so by far i understood that the electrons are in their ground state ,and the induced current due to the changing magnetic field does not decay...
remains for long ... hence what i can interpret out of this is that current will remain constant so the magnetic field ( net ) should continue to exist ...but the effect is gone as soon as the magnetic field is removed...
so where is the error in this interpretation...

please do explain...
 
  • #16
I haven't seen Lenz's Law discussed in this post. Lenz's Law is foundational to explain diamagnetism.
The external magnetic field induces a current in the orbiting e- in such a way that the magnetic field produced by the e- opposes the direction of the external field. Hence the repulsion force and the negative magnetic susceptibility value for all diamagnetic material.
 

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