# What substance could stop a magnetic field? [closed]

I've seen in TV shows with an MRI machine that the characters are behind a glass screen, with things like computers and metal things in there. Is this something that actually blocks the magnetic field or is this just because the MRI magnet field only extends enough not to affect the computers and others in the room? What material is this that is able to stop a magnetic field?

Also, if this material isn't real, what material or substance could block the magnetic field other than thickness of the substance?

• Heard of a Faraday Cage? – AndreiROM Oct 5 '16 at 14:40
• What does it have to do with Worldbuilding? Also, -1 is from me, because it lacks any signs of research effort in the question. – Mołot Oct 5 '16 at 14:55

Magnetic shielding is absolutely real. Hollywood probably gets it wrong, because they do that, but it is a real kind of engineering.

Wikipedia explains it. To summarise, it's easiest if you think in terms of magnetic lines of force. These aren't real, but they are a very useful model for thinking about magnetic fields.

A magnetic shield is made out of a material with high "magnetic permeability", which are always metal alloys, usually mostly nickel and iron. The lines of force prefer to go through the shield, rather than the air, and this reduces the strength of the magnetic field outside the shield. A magnetic shield is usually made in several layers, with gaps in between them, because it becomes less effective at very low and very high field strengths.

The example you cited is due to the fact that magnetic fields fall off quickly not because they are shielded.

The strength of a magnetic field is proportional to 1 / (d^2)

Where d is the distance between the source and the point in question.

so double the distance cut the force in half Try with this with a magnet at home. Two magnets touching each other can take several pounds of force to pull apart by 2 inches apart have no noticeable pull.

So an mri machine that pulls with 10s of pounds inside the body of the machine when it is on pulls with a few pounds a foot away and a few tenths of a pound 2 feet away. by the time you get a full yard away you couldn't feel it.

TLDR Magnetic fields fall off very quickly with distance MRS machines are not shielded just a yard or two of distance negates the effect

There's no such thing that stops magnetic field.However if we assume there's some material which can block magnetic field,then it is only possible if we have magnetic monopole (which is impossible). But we can neglect its effect being in the Faraday cage in which current circulated around it,which produce magnetic field which further interfere with other magnetic field which neglect its effect in the cage