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.

法拉第电磁感应定律的积分形式的更有趣的应用之一是轮廓随时间变化的开放表面。为此经常使用的理论示例是由两个平行的导电轨形成的轨道。轨道之间的平面由一端的电压表界定，而另一端的横越轨道并与之接触的活动导电棒界定了边界。均匀的磁场在该表面垂直的任何地方。当钢筋穿过该磁场，改变轮廓和封闭区域时，它会在导轨之间感应出电压。当然，该理论示例是一种理想化，其中包含不切实际或不可能的元素，例如整个空间的均匀磁场，并且没有来自外部源的任何干扰。在本文中，我们将为该理论示例提供实际的实验实现。轨道是模型铁轨的长度，磁场由一串强大的钕磁铁提供。电池驱动的电动汽车沿轨道拖动短路杆，并且在示波器上显示导轨之间的电压。实验中必须存在的近似值以仍然可以与理论进行良好比较的方式进行说明。还介绍了对基本实验的修改，这些修改提供了对法拉第定律的进一步理解。导轨之间的电压将显示在示波器上。实验中必须存在的近似值以仍然可以与理论进行良好比较的方式进行说明。还介绍了对基本实验的修改，这些修改提供了对法拉第定律的进一步理解。导轨之间的电压将显示在示波器上。实验中必须存在的近似值以仍然可以与理论进行良好比较的方式进行说明。还介绍了对基本实验的修改，这些修改提供了对法拉第定律的进一步理解。