The Metal Detector Metal detectors use induced currents to sense the presence of

Question

The Metal Detector
Metal detectors use induced currents to sense the presence of any metal-not just magnetic materials such as iron. A metal detector, shown in the figure, consists of two coils: a transmitter coil generates an oscillating magnetic field along the axis and an oscillating induced current in the receiver coil.

If a piece of metal is placed between the transmitter and the receiver, the oscillating magnetic field in the metal induces eddy currents in a plane parallel to the transmitter and receiver coils. The receiver coil then responds to the superposition of the transmitter's magnetic field and the magnetic field of the eddy currents. Because the eddy currents attempt to prevent the flux from changing, in accordance with Lenz's law, the net field at the receiver decreases when a piece of metal is inserted between the coils. Electronic circuits detect the current decrease in the receiver coil and set off an alarm.

Part 1-
Why won't the metal detector detect insulators?
(a) Insulators block magnetic fields.
(b) No eddy current can be produced in an insulator.
(c) No emf can be produced in an insulator.
(d) An insulator will increase the field at the receiver.

Part 2 -
Suppose the magnetic field from the transmitter coil in the figure points toward the receiver coil and is increasing with time. As viewed along this axis, what are the induced currents?
(a) Clockwise in the metal, clockwise in the receiver coil.
(b) Clockwise in the metal, counterclockwise in the receiver coil.
(c) Counterclockwise in the metal, clockwise in the receiver coil.
(d) Counterclockwise in the metal, counterclockwise in the receiver coil.

Explanation / Answer

Part 1: The answer is ( c ) This means the insulators not passes the current through them. So there is no emf can be produced in the insulator. Part 2: The answer is ( c ) This means the current produced is in counterclock wise in the metal. By using Ampere thumb rule we can consider like the above.

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