單項選擇題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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1.單項選擇題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

2.單項選擇題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

4.單項選擇題Sparking at the brushes of a running motor could be an indication of ().

A.normal operation
B.a dirty commutator
C.increased brush capacity
D.water vapor absorption

5.單項選擇題If a DC motor runs hot, the cause may be ()

A.high mica condition
B.low ambient temperature
C.clogged ventilation ducts
D.an open in the shunt field