Electrical Basic Questions 6

Electrical Basic Questions 6

1.In a D.C. shunt motor, speed is
A. independent of armature current
B.directly proportional to the armature current
C. proportional to the square of the current
D. inversely proportional to the armature current

ANSWER : : independent of armature current

2.The type of D.C. motor used for shears and punches is

A.  shunt motor
B. series motor
C. differential compound D.C. motor
D. cumulative compound D.C. motor

ANSWER : : cumulative compound D.C. motor

3.If a D.C. motor is connected across the A.C. supply it will

A. run at normal speed
B. not run
C. run at lower speed
D. burn due to heat produced in the field winding by .eddy currents

ANSWER : : burn due to heat produced in the field winding by .eddy currents

4.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

ANSWER : : more than full-load current

5.Differentially compound D.C. motors can find applications requiring

A. high starting torque
B. low starting torque
C. variable speed
D. frequent on-off cycles

ANSWER : : low starting torque

Electrical Basic Questions 6

6.The speed of a D.C. shunt motor more than its full-load speed can be obtained by

A. decreasing the field current
B. increasing the field current
C. decreasing the armature current
D. increasing the armature current

A NSWER : : decreasing the field current

7.A direct on line starter is used: for starting motors

A. up to 5 H.P.
B. up to 10 H.P.
C. up to 15 H.P.
D. up to 20 H.P.

ANSWER : : up to 5 H.P.

8.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

ANSWER : : Commutator

9.These days D.C. motors are widely used in

A. pumping sets
B. air compressors
C. electric traction
D. machine shops

ANSWER : : electric traction

Electrical Basic Questions 6

11.According to Fleming’s left-hand rule, when the forefinger points in the direction of the field or flux, the
middle finger will point in the direction of

A. current in the conductor
B. resultant force on conductor
C. none of the above
D. force on the conductor

ANSWER : current in the conductor

12.In case of D.C. shunt motors the speed is dependent on back e.m.f. only because

A. back e.m.f. is equal to armature drop is negligible
B. flux is proportional to armature current
C. flux is practically constant in D:C. shunt motors

ANSWER C : flux is practically constant in D:C. shunt motors

13.A D.C. series motor is that which

A. has its field winding consisting of thick wire and less turns
B. has a poor torque
C. can be started easily without load
D. has almost constant speed

ANSWER : : has its field winding consisting of thick wire and less turns

14.When two D.C. series motors are connected in parallel, the resultant speed is

A. more than the normal speed
B. loss than the normal speed
C. normal speed
D. zero

ANSWER : : more than normal speed

Electrical Basic Questions 6

15.If a D.C. motor is to be selected for conveyors, which motor would be preferred ?

A. Series motor
B. Shunt motor
C. Differentially compound motor
D. Cumulative compound motor

ANSWER : : Series motor

16.Starters are used with D.C. motors because

A. these motors have high starting torque
B. these motors are not self-starting
C. back e.m.f. of these motors is zero initially
D. to restrict armature current as there is no back e.m.f. while starting

ANSWER : : to restrict armature current as there is no back e.m.f. while starting

17.Which D.C. motor will be preferred for machine tools ?

A. Series motor
B. Shunt motor
C. Cumulative compound motor
D. Differential compound motor

ANSWER : : Shunt motor

18.The direction of rotation of a D.C. series motor can be changed by

A. interchanging supply terminals
B. interchanging field terminals
C. either of (a) and (b) above
D. None of the above

ANSWER : : interchanging field terminals

19.Which of the following application requires high starting torque ?

A. Lathe machine
B. Centrifugal pump
C. Locomotive
D. Air blower

ANSWER : : Locomotive

Electrical Basic Questions 6

20.For starting a D.C. motor a starter is required because

A. it limits the speed of the motor
B. it limits the starting current to a safe value
C. it starts the motor
D. none of the above

ANSWER : : it limits the starting current to a safe value

21.Which D.C. motor is preferred for elevators ?

A. Shunt motor
B. Series motor
C. Differential compound motor
D. Cumulative compound motor

ANSWER : : Cumulative compound motor

22.What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?

A. The motor will stop
B. The motor will continue to run
C. The armature may burn
D. The motor will run noisy

ANSWER : : The armature may burn

23.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

ANSWER : : the speed will remain almost constant

Electrical Basic Questions 6