陕西科技大学电气专业英语试卷

Exercise 2 一、阅读理解（20points）: Passage one The circuit element used to model the current-resisting behavior of a material is the ① . It is the simplest ② element. George Simon Ohm is credited with formulating the ③ relationship for a resistor based on experiments performed in 1826. This relationship is known as Ohm's Law. Ohm's Law states that the voltage across a resistor is ④ the current flowing through the resistor. The constant of proportionality is the resistance value of the resistor in ohms. The circuit symbol for the resistor is shown in Fig.1. For the current and voltage shown, Ohm's Law is u(t) = Ri(t) (1) where R≥0 is the resistance in ohms. Since R is constant, Eq.(1) is the equation of a straight line. For this reason, the resistor is called a linear resistor. A graph of u(t) versus i(t) for a linear resistor is a line passing through the origin with a slope of R. Resistors whose resistances do not remain constant for different terminal current are known as ⑤ resistors. For such a resistor, the resistance is a function of the current flowing in the device. In reality, all practical resistors are nonlinear because the electrical characteristics of all conductors are affected by environmental factors such as temperature. Many materials, however, closely approximate an ideal linear resistor over a desired operating region. Choose the best answer into the blanks. 1 A. capacitor B. inductor C. resistor D. source 2 A. passive B. active C. linear D. nonlinear 3 A. current-current B. current-voltage C. voltage-power D. current-power 4 A. equal to B. directly proportional to C. inversely proportional to D. different from 5 A. linear B. constant C. nonlinear D. time-varying Passage two The effective value of voltage and current is the common method of expressing the Value of AC. This is also known as the RMS value. The effective value of AC is defined in terms of an equivalent heating effect when compared to DC. One RMS ampere of current flowing through a resistance will produce heat at the same rate as a DC ampere. For purpose of circuit design, the peak value may also be needed. For example, insulation must be designed to withstand the peak value, not just the effective value. It may be that only the effective value is known. To calculate the peak value, multiply the effective value by 1.41. Which equation is true?( ) A. Vpeak×1.41=Vrms B. Vpeak÷0.707=Vrms C. Vpeak×0.707=Vrms According to the passage, if the effective value is 100V, the peak value is ( ). A 141 B 70.9 C 70.7 D 14.1 Passage three The higher the frequency of the analogue signal, the more often it must be sampled. However, it is usually adequate to sample a signal at twice its highest frequency. Each binary digit used to show a binary value is known as a bit. The accuracy of conversion is limited by the number of binary bits used by the ADC . If the conversion is made using a four-bit ADC, only sixteen different binary values can be produced. The smallest value is 0000 and the largest is 1111. If an 8-bit ADC is used, then 256 different digital values can be produced. When a measurement of the analogue signal does not coincide with one of these binary values, it must be rounded up or down. 8. If the analogue signal is u=sin(200πt), then the adequate sampling frequency must be more than . A 50Hz. B. 100Hz C. 200Hz D. 50πHz 9. If the conversion is made using a ten-bit ADC, different binary values can be produced. A.1024. B. 256 C. 512 D. 10 10. Explain the underlining word in Chinese according to the article. rounded up or down ( ) 二、学术词组或句子翻译(20points)： ⑴有源滤波器 ⑵机电能量转换 ⑶不间断电源 ⑷模数转换器 ⑸接地故障 ⑹状态变量 ⑺中性点 ⑻差动继电保护 ⑼绝缘配合 ⑽局部放电 ⑾有功功率 ⑿操作中，与交流供电相连的是一次绕组，与负载相连的是二次绕组。 ⒀我们的工作是使电力从它可以取得的地方输送到需用电力的地方去，输电损失要尽可能小。 ⒁本文讨论固态功率器件及其在三相交流感应电机中的应用。 三、根据英文意思找出合适的单词（从列出的单词）（10points） equipotential; inertia; neutral,; short circuit; circuit breaker; lightning; prevent; actuate; carry; customers; cable; contact; relay; increased; armature; protect; power; electricity; rely on; drop out; instantaneous; generator; bearing, magnetic flux A device that responds to a small current or voltage change by activating switches or other devices in an electric circuit. （ ） The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in motion to stay in motion in a straight line unless acted on by an outside force. （ ） A device that supports, guides, and reduces the friction of motion between fixed and moving machine parts. （ ） The rotating part of a dynamo, consisting essentially of copper wire wound around an iron core. （ ） A measure of the quantity of magnetism, being the total number of magnetic lines of force passing through a specified area in a magnetic field. （ ） One that generates, especially a machine that converts mechanical energy into electrical energy. （ ） An automatic switch that stops the flow of electric current in a suddenly overloaded or otherwise abnormally stressed electric circuit. （ ） Of or relating to a particle, an object, or a system that has a net electric charge of zero. （ ） A low-resistance connection accidentally established between two points in an electric circuit. （ ） Having the same electric potential at every point. （ ） 四、英译汉（35points） Passage one When two or more synchronous machines are interconnected, the stator voltages and currents of all the machines must have the same frequency and the rotor mechanical speed of each is synchronized to this frequency. Therefore, the rotors of all interconnected machines must be in synchronism. In a generator, the electromagnetic torque opposes rotation of the rotor, so that mechanical torque must be applied by the prime mover to sustain rotation. The electrical torque (or power) output of the generator is changed only by changing the me