The current flowing first in one direction and then in another is called ____ current.

试卷相关题目

• 1Hydraulic cranes must be properly warmed-up before being operated because ______.

  A.warm-up allows the hydraulic system to become charged with oil

  B.warm-up allows the relief valves to be properly tested

  C.hydraulic strainers operate only during the warm-up period

  D.hydraulic fluid must be at the proper viscosity

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• 2A mooring winch should be equipped with mechanical brakes capable of holding ______.

  A.half the breaking strength of the mooring line

  B.the full breaking strength of the mooring line

  C.the maximum expected tension(张力) of the mooring line

  D.50% over the working tension of the mooring line

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• 3If an anchor windlass has been idle for some time, you should ______.

  A.repack all valve stems

  B.lubricate it prior to use

  C.replace the foundation bolts

  D.balance the warping heads

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• 4The oil in a cargo winch gear box should be sampled periodically(周期性地) to ______.

  A.prevent the gear box from leaking

  B.prevent the oil from becoming inflammable(易燃的)

  C.make sure it has not become contaminated(污染)

  D.make sure the motor bearings are lubricated

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• 5Positive displacement, helical gear(斜齿轮) pumps are well suited for pumping oil because ______.

  A.stuffing boxes eliminate the leakage problems usually associated with other gear pumps

  B.it is not necessary to closely maintain design clearances with this pump

  C.they are essentially self-priming and produce a high suction lift

  D.these pumps are designed with extreme tooth angles

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• 6The frequency of an alternator at a given RPM is determined by the ______.

  A.number of turns of wire in the armature coil

  B.number of magnetic poles

  C.strength of the magnets used

  D.output voltage

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• 7While paralleling two AC generators using synchronizing(同步的) lamps only, both lamps will go dark when the generators are ______.

  A.running at the same speed

  B.grounded

  C.of the same polarity(极性)

  D.in phase

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• 8The load sharing characteristics of two diesel generators operating in parallel are mostly dependent on their governor ______.

  A.load limit settings

  B.idle speed settings

  C.speed limit settings

  D.speed droop settings

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• 9Electric insulation is made of organic substances and so gradually ______with age.

  A.deteriorates

  B.increases

  C.are fouled

  D.becomes better

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• 10The main generators are connected to ______.

  A.distribution boards

  B.section boards

  C.emergency switch boards

  D.main switch boards

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