使食指指向磁场的方向，中指指向电流的方向，那么拇指所指的方向是力的方向
Whereas the copper disk will rotate in the same direction as the rotating magnetic field, it will never reach the same speed as the rotating magnet, because if it did, there would be no relative motion between the two and therefore no current induced in the copper disk. The difference in speed between the rotating magnetic field and the copper disk is known as slip, which is essential to the operation of an induction motor. In induction motors the rotating magnetic field is set up by windings in the stator, and the induced currents are carried by conductorsin the rotor. The rotating horseshoe magnet and copper disk are considerably different in structure from today's induction motor, but the basic principles of operation are the same.
尽管铜圆盘将顺着旋转磁场的方向而旋转，然而它却永远也达不到旋转磁铁的速度，因为如果铜圆盘的速度等于旋转磁铁的速度，那么在两者之间就不存在相对运动因而在铜圆盘中不会感应出电流。旋转磁铁和铜圆盘之间的速度差被称为转差（率），转差（率）对于感应电机的运行是必要的，在感应电机中旋转磁场是通过定子绕组建立的，并且感应电流是由转子导体承载的。旋转U形铁和铜圆盘与目前感应电动机的结构有相当大的不同，但基本工作原理是一样的。 The rotating magnetic field is essential to the functioning of an induction motor. In practical machines this rotating magnetic field is achieved by a
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combination of a space displacement of the windings and a time-phase displacement of the exciting voltage.
旋转磁场对于一台感应电动机来说是必要的。在实际的电机中，旋转磁场是通过绕组在空间上的交替布置和励磁电压在时间相位上的相互交替这两者的结合来实现的。
The rotor is formed from laminated electrical steel punching, and the rotor winding consists of bars contained in slots punched in the laminations. These bars are short-circuited at both ends by a short-circuiting ring. A bar-end ring structure, without the laminated core, is called a squirrel cage, as shown in the Fig.4-2. In small- and medium-horsepower sizes, rotors are made by casting aluminum into the rotor core. In the larger sizes of ac motors, cast-aluminum rotor are not practical, and copper bars are inserted into the slots. Thesecopper bars are short-circuited at both ends by a copper end ring, and the end ring is brazed or soldered onto the bars. Sometimes bronzes or other alloys are used to replace copper in making the cage and end ring. The sizes at which the transition between cast-aluminum and copper rotors takes place varies among rotor manufacturers, but virtually all rotors in motor sizes of several thousand horsepower and above are built with bar-type rotors.
转子是由电工钢冲压叠片形成的，并且转子绕组是由叠片中冲出的槽中的导条组成的。这些导条被两端的短路环所短路。一个没有叠片铁
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心的导条—端环结构被称为鼠笼，如图4－2所示。在中小型电机中，转子是通过在转子槽中铸铝来制成的。在大型交流电动机中，铸铝转子是不实用的，我们将铜导条插入转子槽中。这些铜导体被两端的铜环所短路，并且端环被焊接在导条上。有时我们在制作笼条和端环时用青铜或其他合金来代替铜。铸铝与铜转子之间的尺寸的变化在不同的电机制造商之间有所不同，但实际上功率等于几千马力以及功率大于几千马力的所有电动机的转子都是导条类型的转子。
Another construction feature dependent on motor size is the type of coil winding used. In small- and medium-size ac motors, most coils are random-wound. These coils are made with round wire, which is wound into the stator slots and assumes a diamond shape in the end turns; however, the wires are randomly located within a given coil, and hence the name \For large ac motors and particularly for high-voltage motors, 2300V and above, form-wound coils are used. These coils are constructed from rectangular wire, which is bentinto shape around forms and then taped. The coil is formed to the proper size so that the complete coil can be inserted into the stator slots at the time the stator is wound. Form-wound coils are used for high-voltage windings because it is relatively easy to add extra insulation on the individual coils before inserting them into the stator.
另一个取决于电动机尺寸大小的结构特征是我们所采用的线圈绕组类型。在中小型交流电动机中，大多数的线圈是散绕的，这些线圈是
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由圆导线制成的，它们被绕进定子槽中并且假设其端部线匝为菱形，然而，由于这些导线被随意地放置在给定的线圈中，因此就得到了“散绕”（线圈）这个名称对于大型交流电动机特别是电压等于2300V或大于2300V的高压电动机，我们采用模绕线圈，这些线圈采用矩形截面的导线构成，将它们弯曲成型后缠上绝缘带。在制作定子绕组时，线圈被做成适当的尺寸，以便将整个线圈放入定子槽内。模绕线圈被作为高压绕组使用这是由于在把这些线圈放置入定子槽之前我们可以相对容易地在其单个线圈上增加额外的绝缘。
Most people can formulate a mental picture of a computer, but computers do so many things and come in such a variety of shapes and sizes that it might seem difficult to distill their common characteristics into an all-purpose definition. At its core, a computer is a device that accepts input, processes data, stores data, and produces output, all according to a series of stored instructions.
Computer input is whatever is put into a computer system. Input can be supplied by a person, by the environment, or by another computer. Examples of the kinds of input that a computer can accept include the words and symbols in a document, numbers for a calculation, pictures, temperatures from a thermostat, audio signals from a microphone, and instructions from a computer program. An input device, such as a keyboard or mouse, gathers input and transforms it into a series of
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electronic signals for the computer.
In the context of computing, data refers to the symbols that represent facts, objects, and ideas. Computers manipulate data in many ways, and we call this manipulation processing. The series of instructions that tell a computer how to carry out processing tasks is referred to as a computer program, or simply a \These programs form the software that sets up a computer to do a specific task. In a computer, most processing takes place in a component called the central processing unit (CPU), which is sometimes described as the\of the computer.
A computer stores data so that it will be available for processing. Most computers have more than one location for storing data, depending on how the data is being used. Memory is an area of a computer that temporarily holds data that is waiting to be processed, stored, or output. Storage is the area where data can be left on a permanent basis when it is not immediately needed for processing.
Output is the results produced by a computer. Some examples of computer output include reports, documents, music, graphs, and pictures. An output device displays, prints, or transmits the results of processing. Computers are versatile machines, which are able to perform a truly amazing assortment of tasks, but some types of computer are better suited to certain tasks than other types of computers. Computers can be
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