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At an airport, a perosn is made to walk...

At an airport, a perosn is made to walk through the door wy 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 ?

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The metal detector is made of metallic coils connected with a capacitor. The coils and capacitors are at resonance, when someone carrying metallic things walks through the metal delector, the impendance of the circuit changes. This change in impedance changes the current in the circuit, Which is delected and a sound is emitted.
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