奥鹏教育西安交通大学《专业英语》在线作业6

奥鹏西安交通大学平时在线作业

西交《专业英语》在线作业

Resistors are ( ) elements奥鹏西安交通大学平时在线作业.
A:passive
B:active
C:independent sources
D:dependent sources
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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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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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ON-OFF information can be represented by ( ) signal.
A:a digital
B:an analog
C:a discrete
D:a control
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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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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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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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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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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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The primary winding is connected to ( ).
A:the power source
B:the load
C:the measurement instrument
D:the motor
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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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( ) 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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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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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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Any protection scheme consists basically of ( ).
A:two elements
B:three elements
C:four elements
D:five elements
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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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The distance protection is applied to protect ( ).
A:transformers
B:generators
C:transmission lines
D:buses
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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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( ) is used as coolant in light-water reactors.
A:Gas
B:Organic compound
C:Molten salt
D:Water
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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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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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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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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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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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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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A desktop computer’s sound card sends signals to external ( ).
A:printer
B:speaker
C:Modem
D:keyboard
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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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The notebook computers use ( ) as standard display equipment.
A:CRT display
B:LCDs
C:LED
D:TV screen
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Image clarity on a computer screen is measured with ( ).
A:screen size
B:dot pitch
C:resolution
D:color depth
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( ) 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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##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## .
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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 ## .
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