Measurements and mechanisms of Thomson’s jumping ring

Abstract

Measurements of the phase delay of the current and force on a ring floated on a commonly available Thomson's jumping ring apparatus were performed for phase angles from 12°to 88°. The force and phase data show excellent agreement with a linear inductive model. We find that the demonstration, as usually performed with large highly conducting rings, operates in the inductance-dominated regime at 60-Hz line frequency. Stroboscopic photographs of the jumping ring, for both room-temperature and 78-K rings, confirm that the same time-averaged inductive phase lag mechanism, not an electrical transient, accounts for the jump height. We introduce a simple room-temperature demonstration that illustrates the importance of the phase lag: Despite its greater weight, a stack of thin rings will float higher than a single ring as the inductive phase lag comes to dominate the parallel resistance of the combined rings.

The Phase Shift in the Jumping Ring

“…Tjossem and Cornejo reported phase shifts for a range of frequencies with 60 o at 60 Hz. 10 Both of these estimates are consistent with our results.…”

“…9 Tjossem and Cornejo also reported the force on the ring is greater at the bottom and decreases toward the top. 10 In addition, the latter authors found that the ring takes several cycles, or 0.10 s, to clear the core, using strobe Table I. Results of a kinematics experiment for an aluminum ring 2-cm high, 6 cm in diameter, and 3-mm thick, giving the final velocity leaving the core, the time to jump, number of quarter-cycles (t/0.00417 s), and the average acceleration relative to the acceleration of gravity, g. See Fig.…”

“…6(b), the current may be written as I ring (t) = I max cos (wt -j) [phase shift j ], (10) where I max now is Thus, for a finite phase shift, the net force depends on sin 2 j, 10,12,15 and is zero if j is zero. Of course, F max is a function of the height above the solenoid because of the variation of E max , seen in Fig.…”

Magnet fall inside a conductive pipe: motion and the role of the pipe wall thickness

“…Magnetic braking has also found a number of important applications in the present technology [9]. Both the jumping ring [4,6] and the vertical motion of a small magnet inside a conductive tube are manifestations of Faraday magnetic induction and have recently begun to be studied thoroughly in the laboratory [1][2][3] because of their pedagogical value. It offers, for instance, a good opportunity for a very low cost, honours degree or senior undergraduate experiment on Faraday induction, and it is also an excellent case for illustrating the modelling of an intriguing physics phenomenon.…”

On the linear Active Rejection Control of Thomson's Jumping Ring

“…An interesting MagLev systems is the "Thomson's Jumping Ring" [1], [24], which was created by Elihu Thomson (1853Thomson ( -1937 and consists of an induction coil with a core of some ferromagnetic material and a ring placed in the core (see Figure 1 for a detailed diagram). When an alternating current circulates in the coil, it is induced a current in the ring, the magnetic field due to this induced current opposes the field induced by the coil producing a total repulsive force on the two windings and, in this way, making the ring rises above the core of the coil.…”