单项选择题

A motor enclosure which protects against falling liquids is classified as （）

A.waterproof
B.drip proof
C.spray tight
D.spray proof

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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
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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
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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