Magnetic braking revisited: activities for the undergraduate laboratory

Abstract

This paper revisits the demonstration of Lenz by dropping magnets down a non-magnetic tube. Recent publications are reviewed and ideas for undergraduate laboratory investigations are suggested. Finally, an example of matching theory to observation is presented.

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

“…Note that the zeroth-order expansion of the new approximation (the first term in the square bracket above) reproduces correctly our previous result (equation (5)) given by the dipole approximation. Assuming, once again, that for our magnet μ = 4.716 × 10 −8 T m 3 , equations (28) and (1), can now be used to find the new expression for the induced e.m.f as a function of the vertical coordinate z, and the result appears plotted (curve marked B) in figure 10, jointly with the induced e.m.f. result predicted by the magnetic dipole approximation (curve A).…”

“…Magnetic braking of a falling magnet inside a non-magnetic conductive pipe [1][2][3] and the Thomson jumping ring [4,6] are experiments frequently shown in lecture demonstrations, in open-day physics shows and in science museum exhibits. Both experiences are interesting and capture the students' and public imagination, but they are also difficult for anyone to give a formal account.…”

“…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.…”

Penentuan Nilai Momen Magnet Neodymium Yang Bergerak Di Dalam Pipa Aluminium Dan Kuningan Dengan Metode Analisis Video

“…Penerapan teknologi ini juga dapat digunakan sebagai salah satu metode pembelajaran fisika di sekolah, khususnya materi fisika yang sulit. Dalam penelitian ini, peneliti akan meneliti mengenai redaman magnetik (12). Interaksi antara magnet dengan bahan berkonduktor listrik dapat menyebabkan suatu redaman magnetik.…”

Quantitative analysis of the damping of magnet oscillations by eddy currents in aluminum foil

“…These have included experiments with a magnetically controlled pendulum for observing free and forced oscillations, including nonlinear oscillations and chaotic motion; 1 experiments with strong small magnets and with a current loop to determine the magnetic moment and magnetization of a magnet; 2 a simple arrangement from a suspended magnet for observing and analyzing coupled pendulum and torsional motion; 3 demonstration of Lenz's law by dropping a magnet down a nonmagnetic metal tube where the movement of the falling magnet is affected by eddy currents; 4 and several experiments with two identical small dipole magnets, among them finding the magnitude of the Earth's magnetic field. 5 However, the description of simple experiments with quantitative analysis of eddy currents (e.g., damping of magnet oscillations due to eddy currents) is rarely addressed in physics teaching literature.…”