Does an iron ring shield a static magnetic field?

In summary, the conversation discusses the use of an iron ring to shield a static magnetic field. The question is asked whether this method works and why, considering iron is a ferromagnet. The answer is that the iron ring provides a lower-reluctance path for the magnetic flux, resulting in a lower B field to the right of the ring. This is similar to how electric circuits work, but with different terminology. The magnetic flux is not as well confined to its "conductor" as electric current is to wire.
  • #1
greypilgrim
515
36
Hi.
This picture shows an iron ring shielding a static magnetic field:
hufeisen_feld_ri_magnetfeld_ver.gif

Does this really work, and why? I know that a conductor can shield an electric field (Faraday cage) and a changing magnetic field (Lenz's law), but why would it shield a static field? Especially since iron is a ferromagnet.
 

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  • #2
"It can" is a better answer than "it will". The field lines go through the iron and not the air.
 
  • #3
greypilgrim said:
Hi.
This picture shows an iron ring shielding a static magnetic field:
View attachment 238637
Does this really work, and why? I know that a conductor can shield an electric field (Faraday cage) and a changing magnetic field (Lenz's law), but why would it shield a static field? Especially since iron is a ferromagnet.
The iron ring will provide a lower-reluctance path to the magnetic flux so areas to the right of the ring will have a much lower B field than were the ring absent.

Magnetic circuits are analogous to electric ones: substitute mmf for emf, reluctance for resistance, flux for current, permeability for resistivity, etc. The main difference is that magnetic flux is not nearly so well confined to its "conductor" (a low-reluctance path) as current is to wire.
 
  • #4
You can understand this phenomenon from the perspective of magnetic reluctance. But I think the description from the book is more accurate.
微信图片_20200421141140.jpg
 

1. How does an iron ring shield a static magnetic field?

An iron ring can shield a static magnetic field by creating a closed loop that redirects the magnetic field lines, preventing them from passing through the center of the ring. This is known as the "skin effect" and is due to the high electrical conductivity of iron, which allows it to create a magnetic field that is equal and opposite to the external field.

2. Does the size or shape of the iron ring affect its ability to shield a static magnetic field?

Yes, the size and shape of the iron ring can affect its ability to shield a static magnetic field. A larger ring will have a greater surface area to redirect the field lines, while a smaller ring may not provide enough coverage. The shape of the ring can also impact its shielding ability, as a circular ring is more effective than a square or rectangular one.

3. Can an iron ring shield all types of static magnetic fields?

No, an iron ring can only shield static magnetic fields. It is not effective against dynamic or changing magnetic fields, such as those produced by electric currents or moving objects.

4. How thick does the iron ring need to be to effectively shield a static magnetic field?

The thickness of the iron ring can vary depending on the strength of the magnetic field it is trying to shield. Thicker rings will generally be more effective, but the exact thickness needed will depend on the specific field strength and the size and shape of the ring.

5. Are there any other materials besides iron that can shield a static magnetic field?

Yes, there are other materials that can shield a static magnetic field, such as nickel, cobalt, and some alloys. However, iron is the most commonly used material due to its high magnetic permeability and low cost.

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