1.Resistors are ( ) elements.
2.An electric heater draws 10 A from a 120V line. The resistance of the heater is ( ).
3.The algebraic sum of all voltages around a loop is ( ).
C.sum of voltage rises
D.sum of voltage drops
4.ON-OFF information can be represented by ( ) signal.
5.The process quantizing the continuous values into a binary scale is called ( ).
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
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)
8.The electric machine that operates at speeds above synchronous speed works in ( ) region.
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
10.The primary winding is connected to ( ).
A.the power source
C.the measurement instrument
11.Copper losses are ( ) losses in the primary and secondary windings of the transformer core.
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
13.The generator voltages are usually stepped up to the transmission voltage level by ( ).
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
15.Any protection scheme consists basically of ( ).
16.The protective scheme that senses zero sequence current and operates as necessary is called as ( ).
B.zero sequence protection
C.negative sequence protection
17.The distance protection is applied to protect ( ).
18.The thermal energy of the steam is converted into ( ) energy by the turbine.
19.( ) is used as coolant in light-water reactors.
20.In the form of ( ) the output is continuously fed back and compared with the reference input.
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
D.the output variable
22.The system’s characteristic equation can be used to determine ( ) of a linear time-invariant system.
B.magnitude of the steady-state error
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
24.The Buck(降压式变换器) is a ( ) converter.
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.
26.A desktop computer’s sound card sends signals to external ( ).
27.Data stored in RAM ( ) when the power of the computer is turned off.
A.is held permanently
C.is held temporarily
28.The notebook computers use ( ) as standard display equipment.
29.Image clarity on a computer screen is measured with ( ).
30.( ) that connects at least two networks makes decision about the best route for data.
B.A network card
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## .
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 ## .