Question

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

Answer 1

• Metal detector works on the principle of magnetic induction.
• There is a $transmitter$ coil around the doorway and powered by a current so the region inside the doorway is a magnetic region.
• When a $metallic$ object move in the magnetic region of the doorway then it feels a magnetic field of the transmitter coil so it also generate a magnetic field. This field is called secondary magnetic field and here comes the role of $receiver$ coil in the doorway which $detects$ the secondary field by the metal and current flows through the receiver coil when it feels secondary field and thus enabling the alarm connected to receiver coil to emit a sound.