# Diamagnetism confusion -- Does diamagnetism really have to do with Lenz’s law?

• yymm
yymm
Homework Statement
Does diamagnetism really got to do with Lenz’s law?
Relevant Equations
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In my textbook, and on many websites it says that when placed in a magnetic field and then due to Lenz’s law a magnetic dipole moment is created in atoms and so the material gets attracted to the magnet? But then in the case I bring the magnet close to the material very slowly( so the change in magnetic flux is very low), or I put the magnet there for a long time, stationary, then does that mean the material no longer gets magnetised?

What kind of material? The diamagnetic materials are not attracted.

The answer is that Lenz's law has nothing to do with diamagnetism which is a quantum phenomenon. Lenz's law involves changing magnetic fields. However, all atoms exhibit diamagnetism and do so in steady magnetic fields. The effect has to do with electron orbits excluding magnetic flux. I think your textbook explanation is an attempt to explain diamagnetism as induced eddy currents at the atomic level. As is usual with classical models applied to quantum phenomena, the model falls short.

This Wikipedia article has more information.

hongseok, vanhees71, hutchphd and 1 other person
nasu said:
What kind of material? The diamagnetic materials are not attracted.
sorry I was meant to say repel instead of attract. Thanks for picking it up!

kuruman said:
The answer is that Lenz's law has nothing to do with diamagnetism which is a quantum phenomenon. Lenz's law involves changing magnetic fields. However, all atoms exhibit diamagnetism and do so in steady magnetic fields. The effect has to do with electron orbits excluding magnetic flux. I think your textbook explanation is an attempt to explain diamagnetism as induced eddy currents at the atomic level. As is usual with classical models applied to quantum phenomena, the model falls short.

This Wikipedia article has more information.
Yeah probably. If I haven't studied quantum mechanics yet then is it enough to know that diamagnetic materials gets repelled?

yymm said:
##\dots~## yet then is it enough to know that diamagnetic materials gets repelled?
Enough for what? If you have not studied quantum mechanics but you are worried what will be on the next test, it is probably "enough" to know qualitatively the distinguishing features of diamagnetism, paramagnetism and ferromagnetism.

## What is diamagnetism?

Diamagnetism is a fundamental property of all materials and is characterized by the creation of an induced magnetic field in a direction opposite to an externally applied magnetic field. This causes the material to be repelled by the magnetic field. It is a very weak form of magnetism and is present in all materials, although it is often overshadowed by stronger magnetic effects such as ferromagnetism or paramagnetism.

## How does Lenz's law relate to diamagnetism?

Lenz's law states that the direction of an induced electromotive force (EMF) will always be such that it opposes the change in magnetic flux that caused it. In the context of diamagnetism, the induced currents within the material create a magnetic field that opposes the external magnetic field, which is consistent with Lenz's law. Thus, the diamagnetic response can be seen as an application of Lenz's law at the atomic level.

## Is diamagnetism present in all materials?

Yes, diamagnetism is a universal property of all materials. However, in materials that exhibit stronger magnetic properties such as ferromagnetism or paramagnetism, the diamagnetic effect is often negligible and overshadowed by these stronger effects. In purely diamagnetic materials, such as bismuth or pyrolytic graphite, the diamagnetic effect is more noticeable.

## What causes the diamagnetic effect at the atomic level?

At the atomic level, diamagnetism is caused by the motion of electrons in their orbits around the nucleus. When an external magnetic field is applied, it affects the orbital motion of the electrons, inducing small circular currents. According to Lenz's law, these currents generate a magnetic field that opposes the applied magnetic field, resulting in the diamagnetic effect.

## Can diamagnetism be used to levitate objects?

Yes, diamagnetism can be used to levitate objects, though it requires very strong magnetic fields to counteract the force of gravity. A famous example is the levitation of a small piece of pyrolytic graphite over a set of strong neodymium magnets. This effect is due to the repulsive force generated by the induced diamagnetic currents within the material, which can counteract gravity under the right conditions.

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