What is the physics behind auto door locks?
Although many people think that doors with no lock on them is just magic, but they are sadly mistaken because what is keeping these doors locked are magnets which are located at the top of the door. These locks are called electromagnetic locks and there is a lot of physics behind them. These locks are a huge innovation and convenience and everyone should know just how they work.

These locks consist of an electromagnet and an armature plate. An armature is a coil in which a voltage is introduced by motion through a magnetic field. The magnet is built inside the wall right above the door opening where the plate will be when the door is shut. The locks are based on electromagnetism which basically means that when a current is run through a solenoid, or loop of wires, a magnetic force will be formed. In our case, the magnetic force formed holds the door closed. If you wanted to increase the strength of this force, all you need to do is increase the amount of solenoids. Increasing the magnetic force will allow the lock to withstand more pressure, or be a stronger lock. The current that runs through the solenoids usually comes from the building's electrical system. This is a convenience because if the power were to go out in a crisis situation, the locks would be turned off so everyone can exit the building safely.
external image Electromagnetic_Lock_PML-4100_PML-4101_2200Lbs.jpg

Overall, these locks are a huge innovation and convenience to anyone who uses them, there are no keys needed and they cannot be picked or messed around with. Also, if one wanted to install a keypad lock or finger scanner, they could simply hook it up to these locks. Now that you know the physics behind these locks, spread the word and tell everybody that it is not just magic or the way things are, it is physics.

http://www.ehow.com/how-does_5166799_magnetic-locks-work.html 17 March, 2011
http://www.youtube.com/watch?v=J6H29cdrF10 17 March, 2011
http://www.diytrade.com/china/4/products/1234132/Electromagnetic_Lock_PML-4100_PML-4101_2200Lbs.html 17 March, 2011