单选题According to Ohm’s Law， which of the following is correct？（）A As voltage increases， resistance decreasesB As amperage decreases， resistance decreasesC As resistance decreases， amperage increasesD As resistance increases， voltage increases

A. Loopback Plug

B. Multimeter

C. Power Supply Tester

D. Extension Magnet

The distance between any two meridians measured along a parallel of latitude ______.

A.increases in north latitude and decreases in south latitude

B.decreases as DLO increases

C.increases with increased latitude

D.decreases with increased latitude

A.voltage step-up

B.current step-down

C.current step-up

D.resistance

As the temperature for a given mass of air increases, the ______.

A.dew point increases

B.dew point decreases

C.relative humidity increases

D.relative humidity decreases

With a given load on the cargo hook，the thrust on a cargo boom ______.

A.increases as the angle to the horizontal increases

B.increases as the angle to the horizontal decreases

C.is greatest at an angle of 45° and decreases as the boom is raised or lowered

D.is least at an angle of 45° and increases as the boom is raised or lowered

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！

With a given load on the cargo hook，tension in a single span topping lift ______.

A.increases as the boom's angle to the horizontal increases

B.is at a maximum when the boom is at a 45° angle to the horizontal

C.increases as the boom's angle to the horizontal decreases

D.decreases as the boom's angle to the horizontal decreases

The unit of electrical resistance is the

A.ampere

B.volt

C.watt

D.ohm

The error in the measurement of the altitude of a celestial body，caused by refraction，increases as the ______.

A.horizontal parallax decreases

B.observer's height above sea level increases

C.humidity of the atmosphere decreases

D.altitude of the body decreases