Current and voltage may be in phase
Current may lead the voltage
Current may lag the voltage
All of the above
第1题：
Two buildings on the San Jose campus of a small company must be connected to use Ethernet with a bandwidth of at least 100 Mbps. The company is concerned about possible problems from voltage potential differences between the two buildings. Which media type should be used for the connection（）。
A.UTP cable
B.STP cable
C.coaxial cable
D.fiber optic cable
第2题：
材料：
The field current supply in older machines comes from a lower voltage direct current generator or exciter on the same shaft as the alternator. Modern machines however are either statically excited or of the high-speed brush-less type. The exciter is required to operate to counter the effects of power factor for a given load. The power factor is a measure of the phase difference between voltage and current and is expressed as the cosine of the phase angle. With a purely resistance load the voltage and the current are in phase, giving a power factor of one. The power consumed is therefore the product of voltage and current. Inductive or capacitive loads, combined with resistance loads, produce lagging or leading power factors which have a value less than one.
The power consumed is therefore the product of current, voltage and power factor. The alternating current generator supplying a load has a voltage drop resulting from the load. When the load has a lagging power factor this voltage drop is considerable. Therefore the exciter, in maintaining the alternator voltage, must vary with load current and also the power factor. The speed change of the prime mover must also be taken into account.
问题： The word “machines” in the passage refers to _____.
A.the direct current generator
B.the alternating current generator
C.the exciter
D.the prime mover
Which of the following statements is true according to the passage ?
A.With a purely resistance load, the power factor is zero
B.Inductive loads combined with resistance loads produces leading power factors
C.Capacitive loads combined with resistance loads produces lagging power factors
D.With a purely resistance load, the phase angle is zero
When the load has a lagging power factor this voltage drop is considerable. This sentence means that _____.A.with a purely resistance load, the voltage drops too much
B.there is a considerable voltage drop in the capacitive load combined with resistance load
C.when the load is the capacitive load combined with resistance load, the voltage drops to zero
D.when the load is the inductive load combined with resistance load, the voltage drop is fairly large
The exciter must vary with: ① load current ② the power factor, ③ speed change of the prime mover.A.①
B.②
C.①②
D.①②③
请帮忙给出每个问题的正确答案和分析，谢谢！
第3题：
When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is _____.
A.lagging
B.leading
C.maximum
D.minimum
第4题：
AC voltage to the armature
AC voltage to the field
DC voltage to the armature
DC voltage to the field
第5题：
What does the command show | compare rollback 1 display?（）
第6题：
The number of cycles per second occurring in AC voltage is known as the ______.
A.phase angle
B.frequency
C.wave form
D.half mode
第7题：
Two buildings on the San Jose campus of a small company must be connected to use Ethernet with a bandwidth of at least 100 Mbps. The company is concerned about possible problems from voltage potential differences between the two buildings. Which media type should be used for the connection（）。
第8题：
A.voltage step-up
B.current step-down
C.current step-up
D.resistance
第9题：
What is true if you want to switch undo tablespaces from the current one， called UNDO1， to a new one called UNDO2？（）
第10题：
The alternators are not generating the same voltages and should be adjusted on automatic voltage regulator rheostats
Alternator frequencies are different and should be adjusted on the governor speed controllers
Alternators are out of phase and should be tripped and paralleled again
One alternator has lost one of its phases