The fall of a magnet through a hollow conducting tube is described. Although this experiment is well known, a detailed treatment by means of a circuit analysis allows us to relate the conductivity of the tube to the characteristic parameters of the experiment.

We discuss a technique for measuring the electrical conductivity in metallic tubes based on Faraday’s induction law. A detailed study of magnetic screening in the low frequency approximation leads to expressions that relate the screening coefficient to the geometry, magnetic permeability, and conductivity of the metallic tubes. We discuss experimental results for different tubes.

We report a study on magnetic levitation by induced ac currents in non-magnetic conductors at low frequencies. Our discussion, based on Faraday's induction law, allows us to distinguish the two components of the current responsible for levitation and heating, respectively. The experimental evaluation of the levitation force in a copper ring revealed the accuracy of our analysis, clearly illustrating its asymptotic behaviour versus frequency, and validating it for the qualitative analysis of magnetic levitation and heating in conductors of different shapes such as tubes and discs, composed of collections of conductive loops. The analysis of the results allows precise values of its electrical conductivity to be found. With the help of a simulation technique, this work also reveals the progressive deformation undergone by magnetic induction lines due to magnetic screening when frequency increases.

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