DC Motors Online MCQ Exam Practice - Set 11 - ObjectiveBooks

DC Motors Online MCQ Exam Practice - Set 11

Practice Test: Question Set - 11

1. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
    (A) D.C. series motor
    (B) D.C. shunt motor
    (C) Induction motor
    (D) All of above motors

2. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
    (A) Remain unchanged
    (B) Reduce to one-fourth value
    (C) Increase four folds
    (D) Be doubled

3. Which of the following motors is most suitable for signaling devices and many kinds of timers?
    (A) D.C. shunt motor
    (B) D.C. series motor
    (C) Induction motor
    (D) Reluctance motor

4. In Ward-Leonard control the lower limit of speed is imposed by
    (A) Residual magnetism of the generator
    (B) Core losses of motor
    (C) Mechanical losses of motor and generator together
    (D) All of the above

5. The main disadvantage of the Ward-Leonard control method is
    (A) High initial cost
    (B) High maintenance cost
    (C) Low efficiency at high loads
    (D) All of the above

6. D.C. generators are normally designed for maximum efficiency around
    (A) Full load
    (B) Rated r.p.m.
    (C) Rated voltage
    (D) All of the above

7. The purpose of retardation test on D.C. shunt machines is to find out
    (A) Stray losses
    (B) Eddy current losses
    (C) Field copper losses
    (D) Windage losses

8. When the armature of a D.C. motor rotates, e.m.f. induced is
    (A) Self-induced e.m.f.
    (B) Mutually induced e.m.f.
    (C) Back e.m.f.
    (D) None of the above

9. In D.C. shunt motors as load is reduced
    (A) The speed will increase abruptly
    (B) The speed will increase in proportion to reduction in load
    (C) The speed will remain almost/constant
    (D) The speed will reduce

10. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
    (A) Nothing will happen to the motor
    (B) This will make armature to take heavy current, possibly burning it
    (C) This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
    (D) Motor will run at very slow speed

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