Regarding magnetic shielding....

[harvey1999]

To protect a place from magnetic fields, soft iron is placed around the place, right?
so when magnetic field passes through the soft iron, the soft iron becomes an induced magnet, thereby creating induced fields, which makes no sense as the induced fields would still hit the place. please explain in simple terms? thank you.

 

[Simon Bridge]

Google: faraday cage.

 

[Charles Link]

I've read about different types of iron just a little and it appears some forms of iron, particularly soft iron do not make permanent magnets, but instead have small domains everywhere where inside the iron there are millions of small permanent magnets whose magnetic fields point in every direction and thereby pretty much cancel. Meanwhile, there is another effect (besides ferromagnetism), called diamagnetism, where the free (conduction) electrons in the iron will partially shield any magnetic field, because the free electrons will respond to an applied magnetic field in such a way (.g. making circular orbits) as to generate magnetic fields of their own that oppose the applied magnetic field. In diamagnetism (as opposed to ferromagnetism), the response is opposite that of the applied field. I can't claim to be an authority on this subject, but I do think this is accurate.

 

[Simon Bridge]

The description of diamagnetism and paramagnetism is correct - but not how magnetic shielding works.

Magnetic properties of solids:
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magpr.html

How magnetic shielding works
https://en.wikipedia.org/wiki/Electromagnetic_shielding#How_electromagnetic_shielding_works

 

[Charles Link]

The description of diamagnetism and paramagnetism is correct - but not how magnetic shielding works.

Magnetic properties of solids:
http://hyperphysics.phy-astr.gsu.edu/hbase/solids/magpr.html

How magnetic shielding works
https://en.wikipedia.org/wiki/Electromagnetic_shielding#How_electromagnetic_shielding_works

(Reply deleted because I thought harvey1999 had replied)

 

[Simon Bridge]

Have a look at the links please.

 

[Charles Link]

Have a look at the links please.

Thank you. The screening mentioned in the "links" by the superconductors is particularly interesting. The diamagnetism exhibited by these (i.e. which results in the Meissner effect), is apparently very much stronger than that of ordinary (conductor) materials with free electrons. Additional comment is a system of free electrons, like those found in a conductor, would be expected, by Le Chatlier's principle, to respond in such a manner as to reduce the effect of the applied magnetic field.

 

[Simon Bridge]

If anyone thinks the secondary school model for how conductors can screen out EM is incomplete, they are correct.
However, it is a very good approximation that was demonstrated by Faraday and many others since.
The role of magnetic susceptability in screening magnetic fields should be investigated by the student also - this will be behind the mention of soft iron in post #1 - but, hopefully, the links will have answered the concerns Harvey1999 originally had.

 

[harvey1999]

If anyone thinks the secondary school model for how conductors can screen out EM is incomplete, they are correct.
However, it is a very good approximation that was demonstrated by Faraday and many others since.
The role of magnetic susceptability in screening magnetic fields should be investigated by the student also - this will be behind the mention of soft iron in post #1 - but, hopefully, the links will have answered the concerns Harvey1999 originally had.

thank you