单项选择题
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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相关考题
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单项选择题
When current and voltage reach maximum values at the same time, the power factor is（）
A.minimum
B.maximum
C.leading
D.lagging -
单项选择题
Which is an acceptable means of correcting high mica between commutator bars?（）
A.undercutting
B.sanding
C.burnishing
D.filing -
单项选择题
Generator brushes are staggered to（）
A.reduce current pulsations
B.reduce brush chatter
C.prevent uneven commutator wear
D.allow greater power generation
