單項(xiàng)選擇題

If a voltmeter is connected across a line, it must be protected with a（）

A.shunt
B.high-resistance coil in the armature circuit
C.low-resistance coil in the armature circuit
D.shunt and a coil of high resistance

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單項(xiàng)選擇題

When current and voltage reach maximum values at the same time, the power factor is（）

A.minimum
B.maximum
C.leading
D.lagging

單項(xiàng)選擇題

Which is an acceptable means of correcting high mica between commutator bars?（）

A.undercutting
B.sanding
C.burnishing
D.filing

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