DC Machines MCQs

1) For low reluctance path for the flux in armature, the permeability of the material should be

    a. High

    b. Low

    c. Both (a) and (b)

    d. None of these

2) When the motor runs on no load, then

    a. Back emf is almost equal to applied voltage

    b. Back emf will be greater than applied voltage

    c. Back emf will be less than applied voltage

    d. None of these

3) If the number of conductors and speed of a lap wound generator is doubled then the generated emf will be

     a. Remains same

     b. Twice of the former

     c. Four times of former emf

     d. Half of the former emf

4) D.C. shunt motors are commonly used in

     a. Cranes

     b. Electric traction

     c. Elevators

     d. Lathe machines

5) If a shunt motor is started with its field winding open then

     a. It will rotate at the same speed as that with its field winding closed

     b. It will rotate at less speed as that with its field winding closed

     c. It will rotate at dangerously high speed

     d. None of these

6) Differential compound motors are mainly used in

      a. Drilling machines

      b. Elevators

      c. Electric traction

      d. Not suitable for any practical application

7) Which motor is not suitable for the application of centrifugal pumps?

      a. Shunt motor

      b. Series motor

      c. Cumulative compound motor

      d. Differential compound motor

8) The number of windings on the field of permanent magnet d.c. motor is

      a. More compared to shunt motor

      b. Less compared to shunt motor

      c. Absent

      d. None of these

9) The speed of permanent magnet d.c. motor cannot be controlled by

      a. Flux control method

      b. Rheostatic control method

      c. Electronic circuits

      d. None of these

10) For the protection of d.c. series motor, which starter is commonly used?

      a. Two point starter

      b. Three point starter

      c. Four point starter

      d. None of these

11) Which starter does not provide high speed protection to the d.c. shunt motor?

a. Three point starter                     b. Four point starter

c. Two point starter                         d. None of these

12) Ward-Leonard system is used for

a. Wide range of speed control  b. Very sensitive speed control

c. Both (a) & (b)                                                d. None of these

13) If a resistance is added in series with the field winding of d.c. shunt motor, then its

a. Both speed and torque decreases       b. Both speed and torque increases

c. Speed decreases, torque increases     d. Speed increases, torque decreases

14) Which method is suitable for the speed control, below and above the normal rated speed of d.c. shunt motor?

a. Flux control method                  b. Rheostatic control method

c. Voltage control method           d. All of these

15) In armature voltage control method or rheostatic control method for speed control in d.c. shunt motor, a variable resistance is

a. Added in series with the armature                     b. Added in series with the field

c. Connected across armature                                    d. Both in series with armature and field

16) In the flux control method for controlling the speed of d.c. shunt motor, the speed control is not possible

a. Below normal rated speed                     b. Above normal rated speed

c. Both (a) and (b)                                            d. None of these

17) A series wound motor is also called as universal motor because

a. It will run equally well using either an ac or a dc voltage source

b. It will run well below and above rated speed

c. It can be used in all kinds of applications

d. None of these

18) If a portion of armature current is diverted through the diverter resistance, then the speed of d.c. series motor

a. Remains same              b. Increases        c. Decreases       d. None of these

19) With the increase in temperature, the speed of series and shunt motor will

a. Increase, decrease                     b. Decrease, increase

c. Increase, increase                       d. Decrease, decrease

20) ________ has highest no load speed.

                a. Shunt                               b. Cumulative Compound

                c. Series                               d. Differential Compound

21) Direction of series motor can be changed by

                a. interchanging supply terminal                               b. interchanging field terminal

                c. both                                                                  d. none

22) Speed of d.c. shunt motors are controlled by

a. Flux control method                                  b. Rheostatic control method

c. Voltage control method                           d. All of these

23) In a differential compound d.c. motor, with increase in load, speed

a. Increases                        b. Decreases                      c. Remains same                 d. None of these

24) If a d.c. series motor is started on very light load or on no load then

a. It will run at dangerously high speed which may damage the motor mechanically

b. It will run at very low speed

c. Load does not effect the speed of d.c. series motor

d. None of these

25) The speed armature current characteristics of a d.c. series motor is

a. Rectangular hyperbola                                             b. Linear               c. Parabolic

d. Parabolic till saturation and then linear

26) The starting torque developed in the d.c. series motor and in d.c. shunt motor is

a. High, low         b. High, moderate           c. Moderate, low             d. Moderate, high

27) For a constant torque load, if the armature resistance of shunt motor is doubled (keeping the shunt field constant) then the armature current will

a. Double             b. Get halved                     c. Remain same                                d. None of these

28) he torque developed in d.c. shunt motor is

a. Directly proportional to the armature current

b. Directly proportional to the square of the armature current

c. Inversely proportional to the armature current

d. Inversely proportional to the square of armature current

29) D.C. shunt motor is also called as

a. Constant flux motor                                  b. Constant voltage motor

c. Variable voltage motor                             d. Constant current motor

30) In d.c. machines, equalizer connections are provided in

a. Only wave winding                                    b. Only lap winding

c. Both wave winding and lap winding    d. None of these

31) The armature reaction effect in d.c. machines can be completely neutralized by using

a. Only compensating winding                                   b. Only interpoles

c. Both compensating winding and interpoles   d. None of these

32) Which of the following rule is used to determine the direction of rotation of D.C motor?

a. Coloumb’s Law                                             b. Lenz’s Law

c. Fleming’s Right-hand Rule                       d. Fleming’s Left-hand Rule