The common weakness for a single phase induction motor is it has a very small start torque. To increase its start torque, a strating _____________is connected in series into start winding which will be disconnected when the speed reaches 75% RPM by centrifugal switch.

To change the speed of a DC motor, you can change the applied DC____________. To change the speed of an AC induction motor you must change the ____________ of the AC power supplied.

The stepping size may vary from 0.72° to 90°. This means that a setp motor shaft may turn from 0.72° to 90° for every input_________.

A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another electrical circuit.

A. 对
B. 错

A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to another electrical circuit. It cannot transfer electrical energy from one electrical circuit tomultiple circuits

A. 对
B. 错

The rotating magnetic field is produced by the three-phase current of the statorin the actual three-phase induction motor.

A. 对
B. 错

A 3 phase induction motors do not need a start winding or a Centrifugal switch as it has a RMF (rotate magnetic field). A RMF makes a 3 phase induction motor self-starting

A. 对
B. 错

A transformer can be used for reducing output voltage but also increasing the output voltage. But it’s only on AC. If connect a transformer to DC power supplier the transformer will be over heated

A. 对
B. 错

Select all electromagnetic devices you have learnt from this unit VU22496

A. SCRs
B. Inductors
Chokes
D. Triac
E. Transformers
F. Solenoids
G. Relays
H. Electric bells and buzzers

Match the following advantageswithac, dc, and step motors