單項選擇題If the length of a wire is halved and the cross-sectional area is doubled, the resistance will be ()

A.quartered
B.unchanged
C.doubled
D.quadrupled


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1.單項選擇題AC and DC generators are similar in that they ()

A.both generate alternating voltages
B.both rectify the voltage before delivery
C.are constructed at the same physical size for the same kilowatt rating
D.both supply three-phase power

2.單項選擇題To increase the frequency of an operating AC generator, you should ()

A.increase the field excitation
B.decrease the field excitation
C.increase the number of magnetic poles
D.increase the speed of the prime mover

3.單項選擇題When measuring AC current flow, you must always connect the meter ()

A.in series with the power source and load
B.in parallel with the power source and load
C.insuring correct polarity
D.using the lowest range possible to prevent instrument damage

4.單項選擇題The frequency of an AC generator is adjusted by means of the ()

A.main alternator field rheostat
B.exciter field rheostat
C.prime mover governor control
D.equalizing reactor

5.單項選擇題When the current flow through a copper wire increases, its ()

A.resistance will decrease
B.insulation will bum
C.temperature will increase
D.conductivity will increase