Eddy currents are currents induced in what when crossed by lines of flux from a moving magnet?

• A. A type of aerodynamic flutter
• B. Current induced in a metal cup or disc when crossed by lines of flux from a moving magnet
• C. A DC current in a stationary metal
• D. A magnetic field that remains stationary

Answer: (B)

When magnetic flux through a conductor changes, currents are induced inside the material. These circulating currents, called eddy currents, form in loops within the metal. A metal cup or disc is a classic example because it’s a good conductor and easily exhibits these loops when crossed by the lines of flux from a moving magnet. The changing flux induces an electromotive force around those loops (Faraday’s law), and the currents flow in closed paths. They also produce their own magnetic fields that oppose the change in flux (Lenz’s law), which is why you can feel a braking effect and see heating in the metal. So eddy currents are currents induced in a metal object like a cup or disc when lines of flux from a moving magnet pass through it.