单项选择题
A.relative speed of the rotor poles
B.number of turns of wire in the armature coil
C.strength of the magnets used
D.output voltage
单项选择题 The greatest detrimental effect on idle electrical equipment, such as cargo pump motors, is the（）.
单项选择题 The Wheat-stone bridge is a precision measuring instrument utilizing the principle of changes in（）.
单项选择题 Which of the motors for the devices listed below is fitted with an instantaneous overload relay?（）