At an airport, a person is made to walk through the doorway of a metal detector, for security reasons. If she/he is carrying anything made of metal, the metal detector emits a sound. On what principle does this detector work ?

Explanation

During security check,people are made to walk through a large upright coil of wire which produces a weak A.C. magnetic field . IF we are carrying any significant quantities of iron,the magnetic flux linked with the large coil changes and the induced current generated in coil triggers an alarm.