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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单项选择题

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
C.overheating
D.All of the above

单项选择题

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