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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