A magician places an aluminum ring on a table, underneath which is hidden an electromagnet. When the magician says “abracadabra” (and pushes a switch that starts current flowing through the coil under...

A magician places an aluminum ring on a table, underneath which is hidden an electromagnet. When the magician says “abracadabra” (and pushes a switch that starts current flowing through the coil under the table), the ring jumps into the air. Discuss and explain his “trick.”