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.Management Sciences
Category: D.C. Motors
The condition for maximum efficiency for a D.C. generator is______________?
A. eddy current losses = stray losses
B. hysteresis losses = eddy current losses
C. copper losses = 0
D. variable losses = constant losses
Which motor has the poorest speed control?
A. Differentially compounded motor
B. Cumulatively compounded motor
C. Shunt motor
D. Series motor
In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be______________?
A. 100%
B. around 90%
C. anywhere between 75% and 90%
D. less than 50%
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
Which of the following test can be performed on DC series motor?
A. Swinburne test
B. Hopkinson test
C. Brake test
D. Field test
Hopkinson’s test on D.C. machines is conducted at_______________?
A. no-load
B. part load
C. full-load
D. overload
Sparking, is discouraged in a D.C. motor because_____________?
A. it increases the input power con-sumption
B. commutator gets damaged
C. both A. and B.
D. none of the above
No-load speed of which of the following motor will be highest ?
A. Shunt motor
B. Series motor
C. Cumulative compound motor
D. Differentiate compound motor
If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking?
A. regenerative
B. plugging
C. dynamic braking
D. none of the above
E. any of the above
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