Similarly, dragging and binding are not possible because they are noncontact devices. On the other hand, they dissipate large
amounts of energy, need considerable electric power, and must be supplemented by mechanical brakes.
Application: The Acyclic4 (Homopolar) Generator and Motor—Faraday’s Disk The idea of moving a bar in a
magnetic field is fundamental to all generators in one way or another, as was amply shown in the previous sections. One
particularly simple method is to rotate the bar in a magnetic field rather than translate it. By doing so, the motion is greatly
simplified. The basic idea is shown in Figure 10.23. It consists of a bar, pivoted at one end and rotated in the magnetic field.
Two connections are made: one at the pivot (axis) and one at the moving end. An emf is generated in the bar which is
proportional to the speed of motion. In this case, the output is proportional to the frequency of rotation, but it remains DC. A
more common implementation of the same idea, one that simplifies the connections, is a disk on a shaft rotating in the
magnetic field, as shown in Figure 10.24. The rotating disk acts the same as the rotating bar, but in practical terms, the
connections are easier to make and the device is balanced. This method of generation is one of only a small number of
methods that allow direct generation of DC power.