When the current in a power transmission line is increased,

CDMA for cellular system can be described as follows. As with FDMA, each cell is allocated a frequency （71） , when is split into two parts, half for reverse (mobile unit to base station) and half for （72） (base station to mobile unit). For full-duplex （73） , a mobile unit both reverse and forward channels. Transmission is in the form. of direct-sequence spread （74） , which used a chipping code to increase the data rate of the transmission, resulting is an increased signal bandwidth. Multiple access is provided by assigning （75） chipping codes to multiple users, so that the receiver can recover the transmission of an individual unit from multiple transmissions.

A.ware

B.signal

C.bandwidth

D.domain

All the following is true except that ______．

A.in many places a counter current flows in opposition to the main current close to the bank

B.current can vary with depth of water and large deep draught ships can experience different current effects at differing parts of the hull tend to turn to the wind

C.as speed is reduced，the increased proportion of the ship's vector which is attributable to current will set the ship close to obstructions

D.when close to the berth in a head current，there is a danger that flow inshore of the ship becomes restricted and the ship is subject to interactive forces

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

When landing a lifeboat through heavy surf with a strong current running parallel to the beach（from right to left when facing from seaward）the recommended procedure is to______．

A.approach while coming to the left to take advantage of the current

B.drop an anchor outside the surf line，then pay out anchor line over the bow while the seas carry the boat toward the beach

C.approach slow enough so that the boat can be brought around to meet breaking seas on the bow

D.rig a drogue with tripping line over the bow，back ashore with drogue tripped between breakers

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！

If an attempt is made to hoist a load that exceeds the capacity of an electric winch，an overload safety device causes a circuit breaker to cut off the current to the winch motor ______．

A.when the line pull reaches the rated winch capacity

B.after the line pull exceeds the rated winch capacity

C.after a short build-up of torque

D.immediately

When you are making a high potential test on a piece of repaired electrical machinery, a rise in leakage current indicates _______.

A.good insulation

B.bad insulation

C.high insulation power factor

D.a high slot discharge factor