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西交《专业英语》在线作业

阅读:15 更新时间:2019-07-04 13:22:37

西交《专业英语》在线作业


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1.Resistors are ( ) elements.
A.passive
B.active
C.independent sources
D.dependent sources
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2.An electric heater draws 10 A from a 120V line. The resistance of the heater is ( ).
A.1200?
B.120?
C.12?
D.1.2?
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3.The algebraic sum of all voltages around a loop is ( ).
A.zero
B.indefinite value
C.sum of voltage rises
D.sum of voltage drops
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4.ON-OFF information can be represented by ( ) signal.
A.a digital
B.an analog
C.a discrete
D.a control
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5.The process quantizing the continuous values into a binary scale is called ( ).
A.digital-to-analog conversion
B.digital-to-digital conversion
C.analog-to-digital conversion
D.analog-to-analog conversion
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6.The wide application of operational amplifiers lies in advantage of using ( ).
A.positive feedback networks
B.large open-circuit gain
C.negative feedback networks
D.small output impedance
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7.When an induction motor with 10 poles is supplied by 50Hz three-phase ac power source, the synchronous revolutions per minute is ( ). (Synchronous r/min = 120 f/p)
A.1000
B.900
C.700
D.600
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8.The electric machine that operates at speeds above synchronous speed works in ( ) region.
A.motoring
B.generating
C.plugging
D.stopping
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9.A transformer is a device that can convert one ac voltage to another ac voltage through the action of ( ).
A.an electric circuit
B.a magnetic field
C.an electric field
D.a coupling circuit
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10.The primary winding is connected to ( ).
A.the power source
B.the load
C.the measurement instrument
D.the motor
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11.Copper losses are ( ) losses in the primary and secondary windings of the transformer core.
A.inductive
B.capacitive
C.resistive
D.reactive
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12.( ) can provide an asynchronous link between two ac electric power system with different nominal frequencies.
A.The HVDC (high voltage DC) transmission
B.The EHV (extra-high voltage) AC transmission
C.The AC distribution
D.Generators
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13.The generator voltages are usually stepped up to the transmission voltage level by ( ).
A.series capacitor
B.parallel reactors
C.step-up transformers
D.step-down transformers
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14.The objective of the optimal economic operation of power systems is ( ).
A.to minimize the total production cost
B.to maintain frequency constant
C.to maintain voltages constant
D.to ensure balance between generation and load
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15.Any protection scheme consists basically of ( ).
A.two elements
B.three elements
C.four elements
D.five elements
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16.The protective scheme that senses zero sequence current and operates as necessary is called as ( ).
A.overcurrent protection
B.zero sequence protection
C.negative sequence protection
D.directional protection
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17.The distance protection is applied to protect ( ).
A.transformers
B.generators
C.transmission lines
D.buses
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18.The thermal energy of the steam is converted into ( ) energy by the turbine.
A.electrical
B.mechanical
C.chemical
D.potential
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19.( ) is used as coolant in light-water reactors.
A.Gas
B.Organic compound
C.Molten salt
D.Water
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20.In the form of ( ) the output is continuously fed back and compared with the reference input.
A.continuous control
B.discontinuous control
C.discrete-data control
D.sampled-data control
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21.The overall transfer function is the ratio of the transform of the controlled variable to the transform of ( ).
A.the controlled variable
B.the reference input
C.the feedback
D.the output variable
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22.The system’s characteristic equation can be used to determine ( ) of a linear time-invariant system.
A.the stability
B.magnitude of the steady-state error
C.the controllability
D.the observability
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23.In the root-locus method the actual time response of a system can be obtained by means of ( ).
A.the inverse Fourier transform
B.the inverse Laplace transform
C.the Fourier transform
D.the Laplace transform
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24.The Buck(降压式变换器) is a ( ) converter.
A.voltage step-up
B.current step-down
C.current step-up
D.resistance
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25.Most desktop computers use a separate ( ) as a display device, where notebook computers use a flat panel LCD screen (liquid crystal display screen) that attached to the system unit.
A.keyboard
B.Mouse
C.Monitor
D.hard disk
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26.A desktop computer’s sound card sends signals to external ( ).
A.printer
B.speaker
C.Modem
D.keyboard
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27.Data stored in RAM ( ) when the power of the computer is turned off.
A.is held permanently
B.permanently disappears
C.is held temporarily
D.temporarily disappears
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28.The notebook computers use ( ) as standard display equipment.
A.CRT display
B.LCDs
C.LED
D.TV screen
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29.Image clarity on a computer screen is measured with ( ).
A.screen size
B.dot pitch
C.resolution
D.color depth
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30.( ) that connects at least two networks makes decision about the best route for data.
A.A modem
B.A network card
C.A hub
D.A router(路由器)
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1.##the direct current is useful, it has one great##, that is, there is no easy, economical way to increase or decrease its ##. The alternating current has not this disadvantage.##a special device, it is##to transform a high voltage into a## voltage or a low voltage into a high voltage. The##that we use to transform the voltage is called a##. The alternating current can ##be changed easily into the direct current. The device which can do this is spoken of as a## .
正确答案:

2.There are##inds of current: direct current (DC) and alternating##(AC). A direct current is a current flowing in a##always in one direction.##alternating current is a current##changing its direction of flow. The electric current##through electric##lines is##current. This is because AC is easy to##and more economical when we transmit it over long ## .
正确答案: