Which motor should not be started on no-load ?

Which of the following motors is most suitable for signalling devices and many kinds of timers ?

A. D.C. shunt motor
B. D.C. series motor
C. Induction motor
D. Reluctance motor

To get the speed of D.C, motor below the normal without wastage of electrical energy is used?

A. Ward Leonard control
B. rheostatic control
C. any of the above method
D. none of the above method

Sparking at the commutator of a D.C. motor may result in____________?

A. damage to commutator segments
B. damage to commutator insulation
C. increased power consumption
D. all of the above

Following motor is used where high starting torque and wide speed range control is required?

A. Single phase capacitor start
B. Induction motor
C. Synchronous motor
D. D.C. motor
E. None of the above

As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit____________________?

A. a resistance is connected in series with armature
B. a resistance is connected parallel to the armature
C. armature is temporarily open circuited
D. a high value resistor is connected across the field winding

The main disadvantage of the Ward-Leonard control method is______________?

A. high initial cost
B. high maintenance cost
C. low efficiency at Hght loads
D. all of the above