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西交《专业英语》在线作业
1.[单选题]Resistors are ( ) elements.
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A.passive
B.active
C.independent sources
D.dependent sources
正确答案:——A——
2.[单选题]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?
正确答案:——C——
3.[单选题]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
正确答案:——A——
4.[单选题]ON-OFF information can be represented by ( ) signal.
A.a digital
B.an analog
C.a discrete
D.a control
正确答案:————
5.[单选题]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
正确答案:————
6.[单选题]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
正确答案:————
7.[单选题]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
正确答案:————
8.[单选题]The electric machine that operates at speeds above synchronous speed works in ( ) region.
A.motoring
B.generating
C.plugging
D.stopping
正确答案:————
9.[单选题]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
正确答案:————
10.[单选题]The primary winding is connected to ( ). 无忧答案网，q 761296021
A.the power source
B.the load
C.the measurement instrument
D.the motor
正确答案:————
11.[单选题]Copper losses are ( ) losses in the primary and secondary windings of the transformer core.
A.inductive
B.capacitive
C.resistive
D.reactive
正确答案:————
12.[单选题]( ) 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
正确答案:————
13.[单选题]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
正确答案:————
14.[单选题]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
正确答案:————
15.[单选题]Any protection scheme consists basically of ( ).
A.two elements
B.three elements
C.four elements
D.five elements
正确答案:————
16.[单选题]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
正确答案:————
17.[单选题]The distance protection is applied to protect ( ).
A.transformers
B.generators
C.transmission lines
D.buses
正确答案:————
18.[单选题]The thermal energy of the steam is converted into ( ) energy by the turbine.
A.electrical
B.mechanical
C.chemical
D.potential
正确答案:————
19.[单选题]( ) is used as coolant in light-water reactors.
A.Gas
B.Organic compound
C.Molten salt
D.Water
正确答案:————
20.[单选题]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
正确答案:————
21.[单选题]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
正确答案:————
22.[单选题]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
正确答案:————
23.[单选题]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
正确答案:————
24.[单选题]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
正确答案:————
25.[单选题]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
正确答案:————
26.[单选题]A desktop computer’s sound card sends signals to external ( ).
A.printer
B.speaker
C.Modem
D.keyboard
正确答案:————
27.[单选题]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
正确答案:————
28.[单选题]The notebook computers use ( ) as standard display equipment.
A.CRT display
B.LCDs
C.LED
D.TV screen
正确答案:————
29.[单选题]Image clarity on a computer screen is measured with ( ).
A.screen size
B.dot pitch
C.resolution
D.color depth
正确答案:————
30.[单选题]( ) 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）
正确答案:————
31.[]##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## .
(1)
A.Also
B.Although
C.As
D.For
正确答案:————
(2)
A.meaning
B.thing
C.advantage
D.disadvantage
正确答案:————
(3)
A.resistance
B.capacitance
C.voltage
D.current
正确答案:————
(4)
A.Making
B.Marking
C.Using
D.Having
正确答案:————
(5)
A.possible
B.impossible
C.easy
D.different
正确答案:————
(6)
A.high
B.low
C.large
D.small
正确答案:————
(7)
A.thing
B.machine
C.one
D.device
正确答案:————
(8)
A.transfer
B.transformer
C.change
D.charge
正确答案:————
(9)
A.also
B.easily
C.hard
D.but
正确答案:————
(10)
A.receiver
B.remote
C.rectifier
D.refiner
正确答案:————32.[]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 ## .
(1)
A.one
B.two
C.three
D.four
正确答案:————
(2)
A.conductor
B.coincidence
C.current
D.currency
正确答案:————
(3)
A.current
B.currency
C.semiconductor
D.conductor
正确答案:————
(4)
A.A
B. An
C. The
D. That
正确答案:————
(5)
A.probably
B. periodically
C.timely
D.second
正确答案:————
(6)
A.transmitted
B.transported
C.transformed
D.unlighted
正确答案:————
(7)
A.powder
B.energy
C.poured
D.power
正确答案:————
(8)
A.alternative
B.always
C.alternating
D.alter
正确答案:————
(9)
A.consider
B.console
C.control
D.consent
正确答案:————
(10)
A.time
B.distances
C.way
D.ago
正确答案:————
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