Speed Control of DC motor by Armature Resistance Control

Which torgue is greater?
The following motor definitely has a permanent magnet rotor…………
If the peak value of phase mmf is F (max), the peak value of the rotating field caused by three-phase is…………
In the dc machine the angle between the stator and the rotor field is…………
Speed Of 3-Phase induction motor is controlled from 1 to 2pu using a variable frequency inverter equivalent circuit parameter to vary is...