单项选择题
A.loss of residual magnetism B.absorption of moisture in the insulation C.insulation varnish flaking D.dirt collecting on the windings
The Wheat-stone bridge is a precision measuring instrum...
单项选择题The Wheat-stone bridge is a precision measuring instrument utilizing the principle of changes in（）.
A.inductance B.capacitance C.resistance D.amperage
Which of the motors for the devices listed below is fit...
单项选择题Which of the motors for the devices listed below is fitted with an instantaneous overload relay?（）
A.Fan B.Pump C.Winch D.Machine tool
One factor that determines the frequency of an alternat...
单项选择题One factor that determines the frequency of an alternator is the（）.
A.number of turns of wire in the armature coil B.number of magnetic poles C.strength of the magnets used D.output voltage
