## electrical

### DC Motor MCQ Objective Questions and Answers Page - 3

1.
 In an electric motor , the electromagnetic torque developed is A In opposite direction to both load torque and frictional torque B In the same direction as the load torque but in opposite direction to frictional torque C In the same direction is the load torque and frictional torque D In the same directional as the frictional torque but in the opposite direction to the load torque Answer : A Explanation :
2.
 The torque speed characteristic of a dc shunt motor is A A rectangular hyperbola B A drooping straight line C A parabola D None of the above Answer : B Explanation :
3.
 The horse power obtained from the motor shaft is called the A 1 HP B BHP C Useful output D None of these Answer : B Explanation :
4.
 In a dc motor , the shaft torque is less than armature torque . This is due to A Eddy current loss B Hysteresis loss C Stray loss D All of the above Answer : C Explanation :
5.
 The mechanical output available  at the dc motor shaft is equal to A Electrical power input to motor B Electrical power input less iron and friction losses C Electrical power input less copper losses D Electrical power input less total losses (copper loss, iron loss, friction and windage losses) Answer : D Explanation :
6.
 If Nis the speed of a dc series motor and Ia is the armature current then A
7.
 For small values of armature current Ia, the torque developed by a dc series motor is proportional to A $I_{a}$ B ${I_{a}}^{2}$ C $\sqrt{I_{a}}$ D $\frac{1}{I_{a}}$ Answer : B Explanation :
8.
 For higher values of armature current Ia, the torque developed by a dc series motor is proportional to A $I_{a}$ B ${I_{a}}^{2}$ C $\sqrt{I_{a}}$ D $\frac{1}{I_{a}}$ Answer : A Explanation :
9.
 For higher value of armature current, the speed of a dc series motor is A Proportional to armature current B Proportional to the square of armature current C Inversely proportional to armature current D Constant Answer : D Explanation :
10.
 T and P are the developed electromagnetic torque and the shaft power of a dc series motor. If losses are neglected, then for constant terminal voltage A $T\alpha&space;P$ B
11.
 In comparison to shunt and compound motors a dc series motor develops high torque at start. It is due to its comparatively A Few series turns B Stronger series field C Larger armature current D Smaller armature resistance Answer : B Explanation :
12.
 A fly wheel is normally fitted to A Dc series motor driving a constant torque load B Separately excited dc motor driving pulsed torque load C Cumulatively compound motor driving torque load D Differentially compound motor driving pulsed torque load Answer : C Explanation :
13.
 An electric motor with “constant output power ” will have a torque speed characteristic in the form of a A Straight line through the origin B Straight line parallel to speed axis C Circle about the origin D Rectangular hyperbola Answer : D Explanation :
14.
 T is the load torque of a dc series motor having linear magnetization and negligible armature resistance. Speed of the motor is A Inversely proportional to
15.
 An electric train employing a dc series motor is running at a fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in A Drop in speed and rise in current B Rise in speed and drop in current C Rise in speed and rise in current D Drop in speed with current unaltered Answer : A Explanation :
16.
 In a dc series motor, if armature current is reduced to 70 % of its original value , the torque of the motor will be reduced by A 49% B 51% C 50% D 70% Answer : B Explanation :
17.
 When the torque of a dc series motor is tripled the power approximately increases by A 33% B 50% C 75% D 150% Answer : C Explanation :
18.
 When an electric train is moving down a hill, the dc motor will operate is a dc A Series motor B Series generator C Shunt motor D Shunt generator Answer : B Explanation :
19.
 A dc series motor must not be started on no load because it would A Not develop starting torque B Fail to start without load C Run at dangerously high speed D Draw more current without producing sufficient torque Answer : C Explanation :
20.
 In case of a dc series motor it is possible to have finite no load speed if a resistance is connected across its A Field terminals B Armature terminal C Field and armature together D It is always very high at no load Answer : B Explanation :
21.
 If an additional resistance is connected in series with a dc series motor operating at rated speed of the motor will A Reduce B Increase C Remain unaltered D Oscillate around the normal speed Answer : A Explanation :
22.
 If a resistance is connected across the armature of a dc series motor , it speed for a constant load torque will A Increase B Decrease C Remain unaltered D Become zero Answer : B Explanation :
23.
 Field diverter method of speed control of a dc series motor gives speeds above rated one due to reduction of A Field current B Armature current C Line current D None of these Answer : A Explanation :
24.
 The  field diverter resistance for a dc series motor is of the order of A 0.1 Ω B 10 Ω C 50 Ω D 100Ω Answer : A Explanation :
25.
 The current drawn by a dc motor at starting is A Zero B Very low C Normal D Very high Answer : D Explanation :
26.
 High inrush of current during a starting of a dc motor can  efficiently be restricted to a safer value by increasing the ……..resistance A Shunt field B Armature circuit C Both a and b D None of these Answer : B Explanation :
27.
 The dc motor draws high current at the starting instant due to absence of back emf . In order to prevent this high inrush of current at start, a resistance is connected A Across the field B Across the armature C In series with the armature D In series with the filed Answer : C Explanation :
28.
 For efficient operation of a dc motor, the additional resistance inserted in he armature circuit should be A Increased in steps B Cut out in steps C Left in the armature circuit D Removed immediately after start Answer : B Explanation :
29.
 Three point starters are not suitable for application where speed variation by flux control is required because the motor may A Not start B Run away C Stop at very high speed D Stop at very slow speed Answer : C Explanation :
30.
 If the no –voltage release in a dc motor starter fails to operate on failure of supply, on resumption of supply the motor will A Not start automatically B Start automatically without trouble C Develop very low starting torque D Get damaged due to flow of excessive current in the armature Answer : D Explanation :