Jumping ring

Electromagnetism > Jumping ring

Heinrich Friedrich Emil Lenz (1804 – 1865) was a Russian physicist who formulated the Lenz’s law in 1833. This law specifies the direction in which the e.m.f induced by a time varying magnetic field acts.

Lenz's Law states that the Current Induced in a closed-conducting Coil by a change in the Magnetic Field through the Coil is in a direction such that the Field generated by the Induced Current tends to counterbalance the change in the Magnetic Field that induces the Current.

Lenz’s Law can be pictured by using a Coil connected to a power source and placing a ring on top, Figure 1. When the power is momentariously connected, a strong transient Electric Current flows through the Coil below the Ring. This transient Current in the Coil generates a fast-upward-increasing Magnetic Field, which passes perpendicularly through the stationary Ring. At the bottom, a strong Induced Electric Current is then circulating in the Ring.

Figure 1: The Currents and the Magnetic Fields within a Jumping Ring

The Induced Current in the Ring generates a Magnetic Field opposing the fast-upward-increasing Magnetic Field, as stated in the Lenz’s Law. This opposition creates a repulsion (like two equal poles facing one another) and the Ring jumps upward.

Electromagnetism > Jumping ring