# Lenz's Rule and Ferromagnetism

• TP9109
In summary, Lenz's law will still work with a ferromagnetic ring, but the effects may be different due to lower conductivity and shape of the object. The key principle demonstrated in the video is eddy currents formed through Faraday's law and Ohm's law.
TP9109
Hi,
In this video: , it shows someone with an aluminium ring next to an MRI scanner. He allows the ring to fall over and it falls slowly demonstrating Lenz's law. I understand this but was wondering what would happen if a ferromagnetic ring was used instead of the non-ferromagnetic aluminium ring used in the video.
Obviously I know it would be dangerous and would be attracted to the scanner, but with regards to Lenz's law, in my mind as it accelerates quickly towards the scanner, it would undergo changes in magnetic field so wouldn't a powerful induced magnetic field be induced in the ring (Lenz's law) as it is flying towards the scanner that acts in the opposite direction to the scanner's field?
In other words I am basically asking whether Lenz's law works exactly the same with a ferromagnetic ring as it does with the non-ferromagnetic ring in the video. Because if it does then would you not

TP9109 said:
Summary:: Lenz's law with a ferromagnetic object.

In other words I am basically asking whether Lenz's law works exactly the same with a ferromagnetic ring as it does with the non-ferromagnetic ring in the video.
Lenz’s law does work with a ferromagnetic object.

The key principle demonstrated in this video is actually eddy currents being formed through Faraday's law and Ohm's law. Lenz's law is just the minus sign in Faraday's law, which is what makes it so that the eddy currents work to slow the motion rather than to accelerate it.

For ferromagnetic objects the conductivity is lower so eddy currents are smaller. Also, ferromagnetic objects are usually not a good shape for forming large eddy currents. So the result is that ferromagnetic objects often become projectiles instead of moving slowly.

vanhees71

## 1. What is Lenz's Rule?

Lenz's Rule is a law in electromagnetism that states the direction of an induced current in a conductor will always be such that it opposes the change that produced it.

## 2. How does Lenz's Rule relate to Faraday's Law?

Lenz's Rule is a consequence of Faraday's Law of induction, which states that a changing magnetic field will induce an electric field in a conductor. Lenz's Rule explains the direction of the induced current in the conductor.

## 3. What is ferromagnetism?

Ferromagnetism is a type of magnetism exhibited by certain materials, such as iron, nickel, and cobalt, that have a permanent magnetic moment. This means they can retain their magnetization even after an external magnetic field is removed.

## 4. How do ferromagnetic materials behave in the presence of an external magnetic field?

In the presence of an external magnetic field, ferromagnetic materials will align their magnetic moments in the same direction as the external field, resulting in a net magnetic field that is stronger than the external field. This is known as ferromagnetic saturation.

## 5. How is ferromagnetism different from other types of magnetism?

Ferromagnetism is different from other types of magnetism, such as paramagnetism and diamagnetism, because it is a spontaneous and permanent magnetization that does not require an external magnetic field to be present. It is also much stronger than other types of magnetism, making ferromagnetic materials useful for creating strong magnets.

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