网友您好， 请在下方输入框内输入要搜索的题目：
题目内容
（请给出正确答案）
单选题
Possible phase relationships between voltage and current in an alternating current circuit include which of the following conditions?（）
A
Current and voltage may be in phase
B
Current may lead the voltage
C
Current may lag the voltage
D
All of the above
参考答案
参考解析
解析：
暂无解析
更多 “单选题Possible phase relationships between voltage and current in an alternating current circuit include which of the following conditions?（）A Current and voltage may be in phaseB Current may lead the voltageC Current may lag the voltageD All of the above” 相关考题
考题
When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is _____.A.laggingB.leadingC.maximumD.minimum
考题
The Buck(降压式变换器) is a ( ) converter.
A.voltage step-upB.current step-downC.current step-upD.resistance
考题
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 cableB.STP cableC.coaxial cableD.fiber optic cable
考题
The number of cycles per second occurring in AC voltage is known as the ______.A.phase angleB.frequencyC.wave formD.half mode
考题
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 generatorB.the alternating current generatorC.the exciterD.the prime moverWhich of the following statements is true according to the passage ?A.With a purely resistance load, the power factor is zeroB.Inductive loads combined with resistance loads produces leading power factorsC.Capacitive loads combined with resistance loads produces lagging power factorsD.With a purely resistance load, the phase angle is zeroWhen 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 muchB.there is a considerable voltage drop in the capacitive load combined with resistance loadC.when the load is the capacitive load combined with resistance load, the voltage drops to zeroD.when the load is the inductive load combined with resistance load, the voltage drop is fairly largeThe exciter must vary with: ① load current ② the power factor, ③ speed change of the prime mover.A.①B.②C.①②D.①②③请帮忙给出每个问题的正确答案和分析，谢谢！
考题
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 cableB、STP cableC、coaxial cableD、fiber optic cable
考题
What does the command show | compare rollback 1 display?（）A、the difference between the current candidate configuration and the candidate configuration from one commit agoB、the difference between the current active configuration and the current candidate configurationC、the difference between the current active configuration and the active configuration from one commit agoD、the difference between the current candidate configuration and the archived configuration from one commit ago
考题
What is true if you want to switch undo tablespaces from the current one， called UNDO1， to a new one called UNDO2？（）A、It is NOT possible to switch unless no active transaction exist in UNDO1. B、It is possible to switch to UNDO2； but current active transactions will abort. C、It is possible to switch to UNDO2； current active transactions will be automatically migrated to UNDO2. D、It is possible to switch to UNDO2； only current active transactions will continue to execute inside UNDO1.
考题
单选题The output voltage of a three-phase alternator is regulated by the （）.A
AC voltage to the armatureB
AC voltage to the fieldC
DC voltage to the armatureD
DC voltage to the field
考题
单选题With No~1 and No~2 alternators running in parallel and the KW loads equally shared, one alternator is drawing much higher current than the other.What does this indicate?（）A
The alternators are not generating the same voltages and should be adjusted on automatic voltage regulator rheostatsB
Alternator frequencies are different and should be adjusted on the governor speed controllersC
Alternators are out of phase and should be tripped and paralleled againD
One alternator has lost one of its phases
考题
单选题Voltage will always lead current in a/an （）A
capacitive circuitB
inductive circuitC
magnetic circuitD
resistive circuit
考题
单选题Which is a function of the voltage regulators used with AC generators?（）A
To cut out generators when they are no longer requiredB
To cut in additional generators automatically as requiredC
To divide the KW load equally between generators operating in parallelD
To divide reactive current between generators operating in parallel
考题
单选题What does the command show | compare rollback 1 display?（）A
the difference between the current candidate configuration and the candidate configuration from one commit agoB
the difference between the current active configuration and the current candidate configurationC
the difference between the current active configuration and the active configuration from one commit agoD
the difference between the current candidate configuration and the archived configuration from one commit ago
考题
单选题The （） is a measure of the phase difference between voltage and current and is expected as the cosine of phase angle.A
powerB
efficiencyC
effective powerD
power factor
考题
单选题If the resistance of a circuit is cut in half and the applied voltage is kept constant, the current flow will be （）.A
doubledB
quadrupledC
unchangedD
cut in half
考题
单选题With a （） load the voltage and current are in phase.A
pure resistanceB
capacitiveC
inductiveD
None of the above
考题
单选题With a purely resistance load the voltage and current are in phase, giving a power factor of （）.A
oneB
less than oneC
more than oneD
negative one
考题
单选题When voltage and current developed in an AC circuit reach their peak values at the same time, the power factor is （）A
laggingB
leadingC
maximumD
minimum
考题
单选题Line losses in a distribution circuit are kept to a minimum by （）.A
adding rubber insulation conductors to the circuitB
using higher current and lower voltage increasing theC
number of thermal relays in the circuitD
using higher voltage and lower current
考题
单选题What is true if you want to switch undo tablespaces from the current one， called UNDO1， to a new one called UNDO2？（）A
It is NOT possible to switch unless no active transaction exist in UNDO1. B
It is possible to switch to UNDO2； but current active transactions will abort. C
It is possible to switch to UNDO2； current active transactions will be automatically migrated to UNDO2. D
It is possible to switch to UNDO2； only current active transactions will continue to execute inside UNDO1.
考题
单选题With a purely （） load the voltage and current are in phase, giving a power factor of one.A
inductiveB
resistanceC
combinedD
capacitate
考题
单选题When current and voltage reach maximum values at the same time, the power factor is（）A
minimumB
maximumC
leadingD
lagging
考题
单选题The power factor is a measure of the phase difference between voltage and current and is expressed as the（） of the phase angle.A
sineB
cosineC
tangentD
cotangent
考题
单选题Reduced voltage applied to a motor during the starting period will （）.A
result in decreased acceleration time onlyB
lower the starting current and increase accelerating timeC
cause a greater starting torqueD
increase the starting current and pump capacity
考题
单选题The alternating current generator supplying a load has a voltage drop resulted from the loadWhen the load has a lagging power factor this voltage drop （）.A
is smallB
may be neglectedC
is usefulD
is considerable
考题
单选题A fuse that blows often should be replaced only with a fuse of （）.A
the recommended current and voltage ratingB
higher current and voltage ratingC
higher current and lower voltage ratingD
lower current and higher voltage rating
考题
单选题A transformer in an electric circuit serves to （）A
generate its own electrical powerB
transform electrical energy into mechanical energyC
increase or decrease circuit voltage as requiredD
convert AC current to DC current
热门标签
最新试卷
