## electrical

### DC Motor MCQ Objective Questions and Answers Page - 1

1.
 In the block diagram of a separately excited dc motor how does the armature induced emf appear as ? A Positive feedback B Negative feedback C Disturbance input D Output Answer : B Explanation :
2.
 A 220 V dc machine has an armature resistane of 1Ω. If the full load current is 20 A , the difference of induced voltage, when the macine is running as a motor and generator is A 20 V B 0 V C 40 V D 60 V Answer : C Explanation :
3.
 The current drawnby a 220 V dc motor of armature resistance 0.5Ω and back emf 200V is A 40 A B 44 A C 400 A D 440 A Answer : A Explanation :
4.
 The current drawn by a 120 V dc motor with back emf of 110 V and armature resistance of 0.4Ω is A 4 A B 25 A C 275 A D 300 A Answer : B Explanation :
5.
 In a dc motor energy conversion would not have been possible but for A Input energy from the supply B Production of back emf in the armature C Use of commutator D Rotation of the machine Answer : B Explanation :
6.
 With the increase in speed of a dc motor A Both back emf as well as line current increase B Both back emf as well as line current fall C Back emf increases but line current falls D Back emf falls and line current increases Answer : C Explanation :
7.
 If the back in a dc motor vanishes suddenly, the motor will A Start hunting B Burn C Run at very high speed D Run at very slow speed Answer : B Explanation :
8.
 The output power of any electrical motor is taken from the A Armature B Field C Coupling mounted on the shaft D Motor frame Answer : C Explanation :
9.
 The armature shall must be able to withstand A Any unbalanced magnetic pull on the armature core B Twisting strains due to transmission of torque C Bending moment due to weight of the armature  and commutator D All of the above Answer : D Explanation :
10.
 The output indicated on the name plate of any motor is always the A Gross power B Power drawn in kVA C Power drawn in kW D Output power at the shaft Answer : D Explanation :
11.
 A thicker wire is used in dc series motor  filed winding than that in a dc shunt motor. A To create more flux B To reduce resistance C To carry large load current D Both (b) and (c) Answer : D Explanation :
12.
 In case of a conductively compensated dc series motor , the compensating winding is provided A In series with the armature winding B In parallel with the armature winding C In parallel with the field winding D As a separate unit Answer : A Explanation :
13.
 The dc compounded motors are generally A Level compounded B Cumulative compound C Differential compound D None of these Answer : B Explanation :
14.
 In a dc compounded motor the filed regulator is provided to A Control the flux B Limit the armature current C Demagnetize filed partially D None f the above Answer : A Explanation :
15.
 The direction of rotation of a dc motor can be determined by A Fleming’s right hand rul B Fleming left hand rule C Lenz’s law D Ampere law Answer : B Explanation :
16.
 The direction of rotation of a dc shunt motor can be reversed by interchanging A The supply terminals B The filed terminals only C The armature terminals only D Either field or armature terminals Answer : D Explanation :
17.
 When the supply terminals of a dc shunt motor are interchanged A The motor will stop B The motor will run at its normal speed in the same direction as before C The direction of rotation will reverse D The motor will run much faster in the  same direction . Answer : B Explanation :
18.
 The direction of rotation of a dc series motor can be reversed A By interchanging supply terminals B By interchanging field terminals C Either by interchanging supply terminals or by interchanging field terminals D By interchanging supply terminals as well as field terminals . Answer : B Explanation :
19.
 The direction of rotation of a dc compound motor can be reversed by interchanging ___________connections A Armature B Series field C Shunt field D Armature and series field both Answer : A Explanation :
20.
 The speed of a dc motor is A directly  proportional to back emf and flux B directly proportional to it back emf and inversely proportional to flux C inversely proportional to both back emf and flux D directly proportional to flux and inversely proportional to back emf Answer : B Explanation :
21.
 The speed of a dc shunt motor supplying a load at its rated speed can be reduced by A Connecting an additional resistance in the armature circuit B Connecting an additional resistance in the field circuit C Increasing the applied voltage D Any of the above methods Answer : A Explanation :
22.
 A Dc shunt motor is operating at no load. If the armature is shunted by a resistance its speed will A Increase B Decrease C Remain the same D Be unpredictable Answer : C Explanation :
23.
 The shunted armature control method of speed control for dc shunt motors is A Less expensive B Less wasteful C Suitable for rapidly changing loads D None of the above Answer : C Explanation :
24.
 The armature voltage control is considered suitable for a dc motor driven at constant A Torque B Speed C Power D Current Answer : A Explanation :
25.
 For a constant supply voltage, what are the effects of inserting a series resistance in the filed circuit of a dc shunt motor, on its speed and torque ? A Speed will decrease and the torque will decrease B Speed will increase and the torque will increase C Speed will increase and the torque will decrease D Speed will decrease and the torque will increase Answer : C Explanation :
26.
 In a Ward Leonard drive, if the filed current of the dc generator is suddenly reduced, the controlled dc motor operates A Still in the motoring mode B In dynamic braking mode C In counter current braking mode D In regenerative braking mode Answer : D Explanation :
27.
 Ward Leonard system for  controlling the speed of a dc motor is used where A the  speed in both the directions is required B very fine speed control over the whole range from zero to normal speed is required C the accuracy is speed control is required D all of the above Answer : D Explanation :
28.
 variation in speed by Ward Leonard control of dc motors occurs due to variation in A armature voltage B field C field diverter D armature resistance Answer : C Explanation :
29.
 No load speed of which of the following motor will be highest? A Shunt motor B Series motor C Cumulative compound motor D Differentiate compound motor Answer : B Explanation :
30.
 No load speed of which of the following motor will be highest? A Shunt motor B Series motor C Cumulative compound motor D Differentiate compound motor Answer : B Explanation :
31.
 The direction of rotation of a DC series motor can be changed by A Interchanging supply terminals B Interchanging field terminal C Either of (a) and (b) above D None of the above Answer : B Explanation :
32.
 Which of the following application requires high starting torque? A Lathe machine B Centrifugal pump C Locomotive D Air blower Answer : C Explanation :
33.
 If a D.C motor is to be selected for traction motor would be A Series motor B Shunt motor C Differentially compound motor D Cumulative compound motor Answer : A Explanation :
34.
 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 : B Explanation :
35.
 Which D.C motor will be preferred for constant speed line shafting? A Cumulative compound motor B Differentially compound motor C Shunt motor D Series motor Answer : C Explanation :
36.
 Differentially compound D.C motors can find applications requiring A High starting torque B Low starting torque C Variable speed D Frequent on-off cycle Answer : B Explanation :
37.
 Which D.C motor is preferred for elevators? A Shunt motor B Series motor C Differential compound motor D Cumulative compound motor Answer : D Explanation :
38.
 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 Movement of conductor C Resultant force on conductor D None of the above Answer : A Explanation :
39.
 If the field of D.C shunt motor gets depend while motor is running A Speed of the motor will be reduce B The armature current will reduce C The motor will attain dangerously high speed D The motor will continue to run at constant speed Answer : C Explanation :
40.
 Starter are used wit 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 motor is zero initially D To restrict armature current as there is no back e.m.f while starting Answer : D Explanation :
41.
 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 : C Explanation :
42.
 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 : A Explanation :
43.
 For staring 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 : B Explanation :
44.
 The type of DC 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 : D Explanation :
45.
 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 : D Explanation :
46.
 To get the speed of D.C motor below the normal without wastage of electrical energy …………. is used A ward Leonard control B rheostat control C any of the above method D none of the above method Answer : A Explanation :
47.
 When two D.C series motor are connected in parallel, the resultant speed is A more than the normal speed B less than the normal sped C normal speed D zero Answer : C Explanation :
48.
 The speed of 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 Answer : A Explanation :
49.
 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 : A Explanation :