Magnetic lock operation

Magnetic card lock operation
 
The magnetic card lock relies upon some of the basic concepts of electromagnetism. Essentially it consists of an electromagnet
attracting a conductorwitha force sufficiently largeenough to prevent the door from being opened. In more detailed examination,
 the device makes use of the fact that a current through one or more loops of wire (known as a solenoid) produces a magnetic field.

This works in free space, but if the solenoid is wrapped around a ferromagnetic core such as soft iron the effect
of the field is greatly amplified. This is because the internal magnetic domains of the material align with each other to
greatly enhance the magnetic flux density.