(A) Convert AC to DC
(B) increasing the armature current
(C) Generate uniform torque
(D) Reducing armature resistance
Answer- (C)
2. How is the EMF affected when the armature of a DC motor rotates?
(A) Self-induced EMF
(B) Mutual induced EMF
(C) Back EMF
(D) None
Answer- (C)
3. What happens when the DC motor speed increases?
(A) Back EMF decreases, but line current increases.
(B) Back EMF increases, but line current decreases.
(C) Both the back EMF and the line current decrease.
(D) Both the back EMF and the line current increase.
Answer- (B)
4. Which of the following DC motors has the highest zero load speed?
(A) DC Series
(B) DC Shunt
(C) Cumulative Compound Motor
(D) Differential Compound Motor
Answer- (A)
5. Can the rotation direction of a DC series motor be reversed?
(A) By changing the supply terminal
(B) By changing the field terminal
(C) By changing the armature terminal
(D) By changing the armature or field terminal
Answer- (D)
6. Which of the following applications requires the highest starting torque?
(A) lathe machine
(B) centrifugal pump
(C) Locomotive
(D) Air blower
Answer- (C)
7. With what material is the armature of a DC motor made?
(A) Silicon Steel
(B) mild steel
(C) hardened steel
(D) Cast iron
Answer- (A)
8. What will happen if the field coil of the DC Shunt motor opens while running?
(A) the motor will stop
(B) Motor will run at high speed
(C) Motor will run at low speed
(D) The speed of the motor will remain the same
Answer- (B)
9. In the DC motor, the back EMF is proportional to
(A) Flux
(B) speed
(C) Number of armature conductors
(D) ALL OF THE ABOVE
Answer- (D)
10. Which type of Series Field diverter speed control method is mainly used?
(A) DC Series Motor
(B) DC Shunt Motor
(C) Differential Mixed Motor
(D) Cumulative mixed motor
Answer- (B)
11.DC Motor Series is most suitable for electric traction, because-
(A) Its initial torque is high
(B) It is much cheaper.
(C) It moves very fast.
(D. ALL OF THE ABOVE
Answer- (A)
12. DC machine has 32 coil. The number of commutator segments will be
(A) 32
(B) 18
(C) 64
(D) 40
Answer- (A)
13. Which of the following motor has poor starting torque for the same HP rated and full load speed?
(A) Series Motor
(B) Differential Compound Motor
(C) Shunt Motor
(D) Cumulative Compound Motor
Answer- (B)
14. Which of the following DC motors is always recommended to turn on load?
(A) Series Motor
(B) Shunt Motor
(C) Differentially Compound Motor
(D) Cumulative Compound Motor
Answer- (B)
15. The current flowing in the armature of a DC motor is directly proportional to?
(A) motor speed
(B) Relative torque
(C) armature resistance
(D) Voltage at the terminal
Answer- (B)
16. For which of the following reasons does the cheatring or hassing sound of a DC motor brush come out?
(A) overload
(B) insufficient brush stress
(C) Wrong brush pressure
(D) Short circuit in commutator segment
Answer- (C)
17. A 3 point starter is commonly used with which of the following DC motors?
(A) Series
(B) Shunt
(C) Compound
(D) Both shunt and compound
Answer- (D)
18. The main purpose of a starter in a DC motor is?
(A) increasing armature speed
(B) Limiting armature current
(C) Reducing armature speed
(D) increasing armature flux
Answer- (B)
19. What happens if the DC motor is connected to the AC supply?
(A) Motor will not run
(B) Motor will run at normal speed
(C) The speed of the motor will be low
(D) The heat generated due to vortex current will burn the field coil.
Answer- (D)
20. Armature copper loss in DC machine is proportional to
(A) load current
(B) Load Section 2
(C) 1 / load current
(D) 1 / load section 2
Answer- (B)