一、单选题（共 30 道试题，共 30 分。）V 1. An electric heater draws 10 A from a 120V line. The resistance of the heater is _____.
A. 1200Ω
B. 120Ω
C. 12Ω
D. 1.2Ω
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2. 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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3. 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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4. 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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5. 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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6. The distance protection is applied to protect _____.
A. transformers
B. generators
C. transmission lines
D. buses
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7. Any protection scheme consists basically of _____.
A. two elements
B. three elements
C. four elements
D. five elements
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8. 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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9. _____ 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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10. 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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11. Image clarity on a computer screen is measured with _____.
A. screen size
B. dot pitch
C. resolution
D. color depth
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12. 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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13. _____ 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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14. The notebook computers use _____ as standard display equipment.
A. CRT display
B. LCDs
C. LED
D. TV screen
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15. Resistors are _____ elements.
A. passive
B. active
C. independent sources
D. dependent sources
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16. 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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17. 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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18. A desktop computer’s sound card sends signals to external _____.
A. printer
B. speaker
C. Modem
D. keyboard
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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. 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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21. 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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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. 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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24. The primary winding is connected to _____.
A. the power source
B. the load
C. the measurement instrument
D. the motor
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25. 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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26. 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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27. 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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28. 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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29. 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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30. ON-OFF information can be represented by _____ signal.
A. a digital
B. an analog
C. a discrete
D. a control
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