751. Usually wide and sensitive speed control is desired in case of____________?
A. centrifugal pumps
B. elevators
C. steel rolling mills
D. colliery winders
752. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is______________?
A. 2.36%
B. 4.76%
C. 6.77%
D. 8.84%
753. The armature voltage control of D.C. motor provides____________?
A. constant torque drive
B. constant voltage drive
C. constant current drive
D. none of the above
754. 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
755. The speed of a D.C. shunt motor can be increased by_______________?
A. increasing the resistance in armature circuit
B. increasing the resistance in field circuit
C. reducing the resistance in the field circuit
D. reducing the resistance in the armature circuit
756. If I2 be the armature current, then speed of a D.C. shunt motor is_______________?
A. independent of Ia
B. proportional to la
C. varies as (Ia)
D. varies as la
757. Which motor has the poorest speed control?
A. Differentially compounded motor
B. Cumulatively compounded motor
C. Shunt motor
D. Series motor
758. For a D.C. shunt motor if the excitation is changed_______________?
A. torque will remain constant
B. torque will change but power will remain constant
C. torque and power both will change
D. torque, power and speed, all will change
759. The plugging gives the____________?
A. zero torque braking
B. smallest torque braking
C. highest torque braking
D. none of the above
760. The armature voltage control of D.C. motor provides_____________?
A. constant voltage drive
B. constant current drive
C. constant torque drive
D. none of the above
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