Experimental Study of the Motional Electromotive Force

Experiments are described that develop a pure motional electromotive force detected with a sensitive galvanometer. Old questions are re-examined by an original experimental approach as follows: What are the conditions of relative motion between magnetic field and conductor for developing a motional electromotive force? Unipolar induction is considered when a uniform or symmetrical magnetic field is concerned and special attention is given to the rotation of nonuniform magnetic fields. The results of the latter differ markedly from the former. Concepts of macrostructure and microstructure magnetic fields are considered briefly as applied to the experiments described. References are made to theoretical treatments to clarify the issues, but discussions are kept to the experimental approach with a qualitative rather than quantitative treatment.