In the early 1830s, Michael Faraday performed his seminal experimental research on electromagnetic induction, in which he created the first electric dynamo—a machine for continuously converting rotational mechanical energy into electrical energy. His machine was a conducting disc, rotating between the poles of a permanent magnet, with the voltage/current obtained from brushes contacting the disc. In his first dynamo, the magnetic field was asymmetric with respect to the axis of the disc. This is to be contrasted with some of his later symmetric designs, which are the ones almost invariably discussed in textbooks on electromagnetism. In this paper, a theoretical analysis is developed for Faraday's first dynamo. From this analysis, the eddy currents in the disc and the open-circuit voltage for arbitrary positioning of the brushes are determined. The approximate analysis is verified by comparing theoretical results with measurements made on an experimental recreation of the dynamo. Quantitative results from the analysis are used to elucidate Faraday's qualitative observations, from which he learned so much about electromagnetic induction. For the asymmetric design, the eddy currents in the disc dissipate energy that makes the dynamo inefficient, prohibiting its use as a practical generator of electric power. Faraday's experiments with his first dynamo provided valuable insight into electromagnetic induction, and this insight was quickly used by others to design practical generators.
The author would like to thank his Georgia Tech colleagues Professors Waymond Scott, Jr., John Buck (both from ECE), and Andrew Zangwill (Physics) for their suggestions for improving the manuscript.
I. INTRODUCTION II. ANALYSIS OF FARADAY'S FIRST DYNAMO A. Magnetic scalar potential B. Surface current density C. Faraday's law and the open-circuit voltage III. FARADAY'S OBSERVATIONS IV. REPEATING FARADAY'S EXPERIMENTS V. DISCUSSION: WHAT EVER BECAME OF FARADAY'S FIRST DYNAMO?