Final answer:
A pendulum in a magnetic field is subjected to eddy currents which create magnetic fields opposing its motion, thus creating a damping force that causes it to come to rest sooner.
Step-by-step explanation:
When a pendulum swinging in the magnetic field experiences magnetic damping due to eddy currents, it means that as the pendulum moves through the magnetic field, electric currents are generated within the conductor material of the pendulum bob. This is a consequence of Faraday's Law, which states that a changing magnetic field induces an electromotive force (emf) in a conductor, and these currents are referred to as eddy currents. Eddy currents create their own magnetic fields, which, according to Lenz's Law, oppose the change that produced them. This opposition happens whether the bob is entering or leaving the magnetic field, so drag is experienced in both directions of its swing. As these opposing magnetic fields resist the motion of the pendulum bob, they extract kinetic energy from the pendulum, converting it into thermal energy within the bob, which causes the pendulum to come to rest sooner than it would without the presence of the magnetic field. In contrast, a slotted metal plate or non-conducting bob does not allow for the formation of effective eddy currents, and thus experiences much less magnetic damping.