## electrical

### DC Motor MCQ Objective Questions and Answers Page - 5

1.
 Which of the following dc motors will have least percentage  increase of input current, for the same percentage increase in torque ? A Cumulative compound B Differential compound C Shunt D Series Answer : D Explanation :
2.
 Which of the following dc motors on removal of load will run at the maximum speed ? A Series B Shunt C Cumulative compound D Differential compound Answer : A Explanation :
3.
 Which of the following dc motors has got maximum self relieving property A Shunt B Series C Cumulative compound D Differential compound Answer : B Explanation :
4.
 The dc motor, that has poorest speed regulation is A Cumulative compound B Differential compound C Series D Shunt Answer : C Explanation :
5.
 which motor should not be used for centrifugal pumps A shunt B series C cumulatively compound D differentially compound Answer : B Explanation :
6.
 the ratio of the starting torque to full load torque is minimum in case of A cumulative compound motors B differential compound motors C series motors D shunt motors Answer : B Explanation :
7.
 Which of the following dc motors has almost constant speed over their full load range? A Shunt B Series C Cumulative compound D None of these Answer : A Explanation :
8.
 Which of the dc motors will have highest percentage increase of input current, for the same percentage increase in torque ? A Series B Shunt C Cumulative compound D All equal Answer : B Explanation :
9.
 Which of the following dc motors has least drop in speed from no load to rated full load? A Series motors with interpoles B Series motors without interpoles C Series motors without interpoles D Cumulative compound motors with interpoles Answer : C Explanation :
10.
 A dc motor is to drive a load which is almost nil for certain part of the load cycle nad peak value for short duration. The most suitable dc motor is A Series B Shunt C Differential compound D Cumulative compound Answer : D Explanation :
11.
 On switching a dc motor to dc supply mains it is found to rotate in the direction opposite to that for which it is designed. The dc motor is A Differential compound B Cumulative compound C Series D Shunt Answer : A Explanation :
12.
 A motor used for punching machine is usually subjected to A Full load continuously B Part of full load continuously C No load D Intermittent load Answer : D Explanation :
13.
 For continuously running rolling mills with  intermittent loading the most suitable dc drive is A Dc series motor B Dc shunt motor C Dc differentially compounded motor D Dc cumulatively compounded motor Answer : D Explanation :
14.
 The speed of a dc motor depends upon A Flux per pole B Applied voltage to armature C Voltage drop in armature circuit resistance D All of the above Answer : D Explanation :
15.
 The field flux method of speed control of dc shunt motor is generally used for which one of the following  ? A Constant hp drive below the base speed B Constant torque drive above the abase speed C Constant torque drive below the base speed D Constant hp drive above the base speed Answer : D Explanation :
16.
 The resistance of the field regulator of a dc shunt motor is of the order of A 100 B 10 C 2 D 0.5 Answer : A Explanation :
17.
 The speed of a dc shunt motor can be raised above its rated value by A Inserting an additional resistance in the armature circuit B Inserting an additional resistance in the field circuit C Reducing the applied voltage D Using either of the above methods Answer : B Explanation :
18.
 Which of the following statements associated with field control of dc shunt motors is correct A Speed can be varied below nad above the rated speed to any extent B Speed can be varied above to any extent and below to a certain extent C Speed can be varied above to the extent of satisfactory commutation and below no variation D Speed can be varied above to the extent of satisfactory commutation and below to any extent. Answer : C Explanation :
19.
 A dc shunt motor is supplying a load at its rated speed. The speed can be reduced by A Armature circuit resistance control B Field resistance control C Ward Leonard control D Any of the above Answer : A Explanation :
20.
 in a dc compound motor, 4-point starter is employed A to reduce the field current B to increase the field current C not to affect the current flowing through Hold On coil even when the field current changes D none of the above Answer : C Explanation :
21.
 In a dc compound motor, 4-point starter provides A Over load protection B Under voltage protection C The facility for wide range of speed control by field regulator D All of the above Answer : D Explanation :
22.
 A large dc shunt motor can be started preferably using a A Compensator B Strong field C Weak field D None of these Answer : A Explanation :
23.
 The simplest form of a motor controller is A Relay B Toggle switch C Drum switch D Magnetic switch Answer : B Explanation :
24.
 The most economical method  of electric braking is A Plugging B Dynamic braking with separate excitation C Dynamic braking with self excitation D Regenerative braking Answer : D Explanation :
25.
 The electric braking system employed with dc shunt motors , in which the armature connections are reversed so that the motor tends to run in  opposite direction is called the ____braking A Plugging B Rheostatic C Dynamic D Regenerative Answer : A Explanation :
26.
 Plugging of dc machine is normally executed by A Reversing the field polarity B Reversing the armature polarity C Reversing both field and armature polarity D Connecting the resistance across armature terminals Answer : B Explanation :
27.
 A dc shunt motor, running lightly at  1,000 rpm , is operated under plugging. With plugging connection left as it is the final speed of the motor will be A Zero B 1,000 rpm C -1000 rpm D -2,000rpm Answer : C Explanation :
28.
 In plugging of a dc shunt motor, the resistance is inserted in the armature circuit to A Increase the braking  torque B Stop the motor quickly C Limit the armature current D Have a shorting effect on the shunt field Answer : C Explanation :
29.
 The plugging provides _______ braking torque in comparison to rheostatic and regenerative braking systems A Negligible B Small C Highest D none Answer : C Explanation :
30.
 The electric braking system commonly employed in rolling mills, elevators and  printing presses is A Plugging B Rheostatic C Dynamic D Regenerative Answer : A Explanation :
31.
 In case the back e.m.f. and the speed of a DC motor are doubled, the torque developed by the motor will A Remain unchanged B Reduce to one – fourth value C Increase four folds D Be doubled Answer : A Explanation :
32.
 At the instant of starting when a D.C motor is put on the supply, it behaves like A A highly resistive circuit B A low resistance circuit C A capacitive circuit D None of the above Answer : B Explanation :
33.
 The speed of a D.C motor can be varied by varying A Field current B Applied voltage C Resistance in series with armature D Any of the above Answer : D Explanation :
34.
 Which one of the following is not necessarily the advantage of D.C motors over A.C motors? A Low cost B Wide speed range C Stability D High starting torque Answer : A Explanation :
35.
 For a D.C shunt motor if the excitation is changed A Torque will remain constant B Torque will change but power will remain constant C Torque and power both will changed D Torque, power and speed all will change Answer : B Explanation :
36.
 Which motor has the poorest speed control? A Differentially compounded motor B Cumulatively compounded motor C Shunt motor D Series motor Answer : D Explanation :
37.
 The plugging gives the A Zero torque braking B Smallest torque braking C Highest torque braking D None of the above Answer : C Explanation :
38.
 The armature voltage control of D.C motor provides A Constant voltage drive B Constant current drive C Constant torque drive D None of the above Answer : C Explanation :
39.
 If a D.C motor designed for 40°c ambient temperature is to be used for 50°C ambient temperature, the motor A of lower H.P should be selected B of higher H.P should be selected C can be used for 50°C ambient temperature also D is to be derated by a factor recommended by manufacture and select the next higher H.P motor Answer : D Explanation :
40.
 If the terminals of armature of D.C motor are interchanged, this action will offer following kind of barking A regenerative B plugging C none of the above D any of the above Answer : B Explanation :
41.
 Which of the following motor one will choose to drive the rotary compressor? A D.C shunt motor B D.C series motor C Universal motor D Synchronous motor Answer : D Explanation :
42.
 If the speed of a D.C shunt motor is increased, the back e.m.f of the motor will A Increase B Decrease C Remain same D Become zero Answer : A Explanation :
43.
 Why are the DC motors preferred for traction applications? A Torque and speed are inversely proportional to armature current B Torque is proportional to the armature current C Torque is proportional to the square root of the armature current D The speed is inversely proportional to the torque and the torque is proportional to the square o armature current Answer : D Explanation :
44.
 Which of the following motor have almost constant speed over their full load range? A A.C series motor B D.C shunt motor C Low resistance squirrel cage motor D Both (b) and (c) Answer : D Explanation :
45.
 Which of the following motors is usually used in house-hold refrigerator’s? A D.C shunt motor B D.C series motor C Single-phase induction motor (split phase start or induction run motor) D Reluctance motor Answer : C Explanation :
46.
 Which motor should not be started on no-load? A Series motor B Shunt motor C Cumulatively compounded motor D Differentially compounded motor Answer : A Explanation :
47.
 Ward-Leonard control is basically a A Voltage control method B Field diverter method C Field control method D Armature resistance control method Answer : A Explanation :
48.
 For constant torque drive which speed control method is preferred? A Field control B Armature voltage control C Shunt armature control D Mechanical loading system Answer : B Explanation :
49.
 In Ward-Leonard control the lower limit of speed is imposed by A Residual magnetism of the generator B Core losses of the motor C Mechanical losses of motor and generator together D All of the above Answer : A Explanation :
50.
 For constant torque drive which speed control method is preferred? A Field control B Armature voltage control C Shunt armature control D Mechanical loading system Answer : B Explanation :