I don't understand this phenomenon. I think when current flows through the rings. Magnetic poles are induced at the ends of the coil. When the upper end is north pole, south pole is induced at the aluminium ring. When the upper end is south pole, north pole is induced at the aluminium ring. Then, the ring should be attracted to the coil firmly. Is it?
- 天同Lv 710 年前最愛解答
No, you are wrong.
When the upper end of the coil is a "North" pole, magnetic field lines are running vertically upward through the coil and the aluminium ring. Because there is an increase of magnetic flux through the ring, current is induced on the ring.
By Lenz's Law, the induced current must flow in a direction so as to reduce the increase of the magnetic flux. That is, the magnetic flux produced by the induced current in the ring is in opposite direction to that produced by the coil, i.e in a vertically downward direction. The lower end of the ring is thus a "North" pole, and repulsion occurs between the coil and ring.