i need your help of how to design a simple magnetic lock. this is similar to the one usually seen at the backside of office doors.i just need the idea of howto go about designing it.

lihle

 

U'll need an electro-magnet and some soft metal same size as the magnet.

Some way to enter user info, like a keycard or Keypad with a combination lock. Some skills in building this kinda stuff.

Easy

 

How strong does the locking force have to be?

 

Have a look about 1/2 way down this page:
http://www.coolmagnetman.com/magelect.htm
Seems to be a good way to get decent force with not much power.