Metal detectors, like the ones used at airports, are activated by A. alternating current. B. magnetic fields. C. electromagnetic induction. D. electric fields.

Option (C)

Explanation:

A metal detector is usually referred to as a device that is used to determine the presence of metals. It is commonly used for safety purposes, like in the airports and railway stations, where the hidden metals are detected.

These devices are mainly activated by the use of electromagnetic induction. It mainly comprises of one or more number of inducting coils that interact with the elements present on the ground surface and which are metallic in nature.

When the metallic objects come within the zone of existing electromagnetic field, then it eventually attains energy and re-transfer an electromagnetic field of its own.

Thus, the correct answer is option (C).