单项选择题
Universal motors will operate on AC or DC current, and are generally found in （）
A.portable tools
B.large pump motors
C.turbo electric main motors
D.forced draft fans
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An operational amplifier, as used in todays consoles, has a calculated gain of 5This means that when the input changes （）
A.5 volts, the output changes 10 volts
B.10 volts, the output changes 5 volts
C.2 volts, the output changes 10 volts
D.10 volts, the output changes 2 volts -
单项选择题
Electrical failures in motors are caused by the breakdown of insulation, which may be caused by （）
A.penetration of moisture
B.accumulation of dirt
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A three-phase alternator operates at 450 volts with a power factor of 0~8.If the ammeter indicates 250 amperes, what should be the KW meter reading （）.
A.90~0 kw
B.127~27 kw
C.155~70 kw
D.194~85 kw
