An Experimental Demonstration For A Well-Known Example Of Faraday'S Law Of Electromagnetic Induction

One of the more interesting applications of the integral form of Faraday's law of electromagnetic induction is to an open surface whose contour is changing with time. An often-used theoretical example for this is a track formed from two parallel, conducting rails. The planar surface between the rails is bounded by a voltmeter at one end and a moving, conducting bar across and in contact with the rails at the other end. A uniform magnetic field is everywhere normal to this surface. As the bar moves through this magnetic field, changing the contour and the enclosed area, it induces a voltage between the rails. Of course, this theoretical example is an idealization containing impractical or impossible elements, such as a uniform magnetic field throughout space, and a lack of any interference from external sources. In this paper, we present a practical experimental realization for this theoretical example. The rails are a length of model railroad track, and the magnetic field is provided by a string of powerful neodymium magnets. A battery-powered, motorized car drags the shorting bar along the track, and the voltage between the rails is displayed on an oscilloscope. The approximations necessarily present in the experiment are accounted for in a manner that still allows good comparison with the theory. Modifications of the basic experiment that provide additional understanding for Faraday's law are also presented.