electromagnetic door locks: theory of operation?

[mdhurt34]

Hello,


I am not terribly familiar with the physics involved, so I am sure this is a rather elementary question.

(Guidance/pointers to other resources would be greatly appreciated.)

My main question:

What is the theory of operation behind electromagnetic door locks? They seem pretty strong without requiring any sort of fancy power source or controller circuitry.

As in:

http://en.wikipedia.org/wiki/Magnetic_lock

And further, what happens to the "system" as force is progressively applied to the door, and the lock eventually fails?

Sub-questions inspired by the above query, (and my lack of fundamental understanding):
[OL]
[LI]What does the classic (and yet still practically built & used) electromagnet "device" look like, and what are it's components?[/LI]

[LI]What exactly do those pretty "flux lines" in popular magnetic illustrations mean?[/LI]

[LI]How would you calculate the "force" acting on a stationary ball bearing at both 10 cm and 20 cm away from our classic electromagnet?[/LI]

[LI]What happens in a system as a ball bearing enters the field generated by the above classic electromagnet powered by a simple DC power source? (what starts to change with regard to: force, position, current, voltage, etc.)[/LI]

[LI]What must happen for a "constant force" to be imparted to a ball bearing as it travels through some defined region of the electromagnet's field? (For simplicity, let's assume it's headed directly towards the magnet, and only due to the attracting force.)[/LI]
[/OL]

 

[bozzah]

the current when passed through a wire creates magnetic field arount the wire. When wire is wrapped around the iron core, magentic vector does not cancel but is parallel, hence the power of the field.
maglocks operate on 12 to 24 V DC. They need constant source of current to remain locked. If you loose the power lock will open (fail-safe). Maglocks are genrally rated 300-1200 pounds of pulling force.

http://en.wikipedia.org/wiki/Electromagnet