A disc magnet has its north and south poles on its faces. To achieve levitation of a model maglev train, how should the magnets be arranged on the train and track?

• A. flat, so that the north pole of the magnets on the train points up and the north poles of the magnets on the track point down
• B. flat, so that the north pole of the magnets on the train point up and the north poles of the magnets on the track point up
• C. on edge, so that the north poles of the magnets on the train point to the front and the north poles of the magnets on the track point toward the rear
• D. on edge, so that the north pole of each magnet on the train and on the track point toward the rear of the train

Answer: (A)

The lifting effect comes from repulsion between like poles facing each other. With a disc magnet that has the poles on its faces, placing the magnets flat means the facing surfaces determine the interaction. If the train’s magnets are oriented so the top face is north, the bottom face becomes south. To get repulsion that pushes the train upward, the track magnets must present the same pole (south) on the top-facing surface. That happens when the track magnets have the north pole on the underside, so the top surface facing the train is south. Then the train bottom (south) and track top (south) repel, producing lift. The other arrangements either create attraction or misalign the force, so they don’t levitate effectively.