Chapter 37, Problem 27A

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. Explain his trick.

To determine

To explain: the ring jumps into the air when the current starts flowing through the coil.

Answer to Problem 27A

When the current starts flowing there will be induced voltage in the aluminum ring and the rings jump into the air.

Explanation of Solution

Introduction:

The electric current produces magnetic field.

When the current passes through the coil when the switched is on, the magnetic field developed, and the voltage induces. This induced voltage opposes the original as per Lenz law.

According to Lenz law, the direction of flow of induced electric current is such that it opposes the change which has induced it. So the aluminum coil starts to move into the air.

Conclusion:

The aluminum ring moves into the air due to induced voltage.