An eddy current is induced in a conducting article by which of the following?

An eddy current is induced in a conducting material primarily by an alternating magnetic field. This phenomenon occurs due to Faraday's law of electromagnetic induction, which states that a changing magnetic field within a closed loop of wire induces an electromotive force (emf) and, consequently, a current. In this context, when the magnetic field alternates, it causes fluctuations that generate circulating currents—known as eddy currents—within the conductor.

Eddy currents form in response to the changes in the magnetic field and flow perpendicular to the direction of the magnetic flux. These currents can result in energy losses in the form of heat, which is why they are often a crucial consideration in applications such as induction heating and electromagnetic braking.

The other options do not generate eddy currents in the same manner. For example, gamma rays are a form of high-energy electromagnetic radiation that does not induce currents in conductors through magnetic fields. Similarly, while piezoelectric forces can generate electrical charges in certain materials due to mechanical stress, they do not create eddy currents since they do not involve magnetic fields or induction processes. Thus, the mechanism of inducing eddy currents is specifically tied to alternating magnetic fields, making this the correct choice.