单项选择题

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

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单项选择题

The unit of electrical resistance is the （）

A.ampere
B.volt
C.watt
D.ohm

单项选择题

Some large A-Cmotors are equipped with heatersThese could be （）
(1)resistance heaters bolted directly to the frame
(2)low voltage windings embedded in the motor windings

A.(1) only
B.(2) only
C.either (1) or (2)
D.neither (1) or (2)

单项选择题

In order to change the direction of rotation of a D-Cmotor （）
(1) the field leads must be changed
(2) the input leads must be changed

A.（1）only
B.（2）only
C.either（1）or（2）
D.neither（1）or（2）