Unveiling the physics of the Thomson jumping ring

TL;DR

This paper introduces a new model and experiments that reveal the complex physics behind the Thomson jumping ring, including electro-dynamics and magnetic interactions, with an accessible setup suitable for educational purposes.

Contribution

The work provides a comprehensive model and low-cost experimental setup to analyze the physics of the jumping ring, making it accessible for educational use and detailed study.

Findings

Successful separation of ring position and time variables

Validation of the theoretical model with experimental data

Insights into the mutual inductance and magnetic field measurements

Abstract

We present a new model, and the validating experiments, that unveil the rich physics behind the flight of a conductive ring in the Thomson experiment, a physics veiled by the fast thrust that impels the ring. We uncover interesting features of the electro-dynamics of the flying ring, e.g. the varying mutual inductance between ring and the thrusting electromagnet, or how to measure the ring proper magnetic field in the presence of the larger field of the electromagnet. We succeed in separating the position and time dependences of the ring variables as it travels upward in a diverging magnetic field, obtaining a comprehensive view of the ring motion. We introduce a low-cost jumping ring set-up that incorporates simple innovative devices, e.g. a couple of pick-up coils connected in opposition that allows us to scrutinize the ring electro-dynamics, and to confirm the predictions of our theoretical model with good accuracy. This work is within the reach of senior students of science or engineering, and it can be exploited either as a teaching laboratory experiment or as an open-end project work.