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

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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