D.C. Motors Multiple Choice Questions And Answers In English -03

1. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
(A) almost negligible
(B) rated full-load current
(C) less than full-load current
(D) more than full-load current
Ans: D

2. 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%
Ans: D

3. In D.C. motor which of the following can sustain the maximum temperature rise?
(A) Slip rings
(B) Commutator
(C) Field winding
(D) Armature winding
Ans: C

4. The speed of a D.C. series motor is
(A) proportional to the armature current
(B) proportional to the square of the armature current
(C) proportional to field current
(D) inversely proportional to the armature current
Ans: D

5. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
(A) Frame
(B) Shaft
(C) Commutator
(D) Stator
Ans: C

6. Which of the following load normally needs starting torque more than the rated torque?
(A) Blowers
(B) Conveyors
(C) Air compressors
(D) Centrifugal pumps
Ans: B

7. The starting resistance of a D.C. motor is generally
(A) low
(B) around 500 Q
(C) 1000 Q
(D) infinitely large
Ans: A

8. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal
to
(A) 100% of the previous value
(B) 50% of the previous value
(C) 25% of the previous value
(D) 10% of the previous value
(e) none of the above
Ans: C

9. The current drawn by the armature of D.C. motor is directly proportional to
(A) the torque required
(B) the speed of the motor
(C) the voltage across the terminals
(D) none of the above
Ans: A

10. The power mentioned on the name plate of an electric motor indicates
(A) the power drawn in kW
(B) the power drawn in kVA
(C) the gross power
(D) the output power available at the shaft
Ans: D

11. Which D.C. motor has got maximum self loading property?
(A) Series motor
(B) Shunt motor
(C) Cumulatively compounded ‘motor
(D) Differential compounded motor
Ans: D

12. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?
(A) Series motor
(B) Shunt motor
(C) Cumulatively compounded motor
(D) Differential compounded motor
Ans: C

13. D.C. series motors are used
(A) where load is constant
(B) where load changes frequently
(C) where constant operating speed is needed
(D) in none of the above situations.
Ans: D

14. 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
Ans: C

15. As -the load is increased the speed of D.C. shunt motor will
(A) reduce slightly
(B) increase slightly
(C) increase proportionately
(D) remains unchanged
Ans: A

16. The armature torque of the D.C. shunt motor is proportional to
(A) field flux only
(B) armature current only
(C) both (A) and (B)
(D) none of the above
Ans: B

17. 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%
(6) 4.76%
(C) 6.77%
(D) 8.84%
Ans: B

18. 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
Ans: A

19. 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
Ans: A

20. The plugging gives the
(A) zero torque braking
(B) smallest torque braking
(C) highest torque braking
(D) none of the above
Ans: C