300 Important DC Motor MCQ Questions & Answers with Explanation | PDF Free Download
1.The mechanical output available at the dc motor shaft is equal to
- AElectrical power input to motor
- BElectrical power input less iron and friction losses
- CElectrical power input less copper losses
- DElectrical power input less total losses (copper loss, iron loss, friction and windage losses)
2.For higher value of armature current, the speed of a dc series motor is
- AProportional to armature current
- BProportional to the square of armature current
- CInversely proportional to armature current
- DConstant
3.In comparison to shunt and compound motors a dc series motor develops high torque at start. It is due to its comparatively
- AFew series turn
- BStronger series field
- CLarger armature current
- DSmaller armature resistance
4.A fly wheel is normally fitted to
- ADc series motor driving a constant torque load
- BSeparately excited dc motor driving pulsed torque load
- CCumulatively compound motor driving torque load
- DDifferentially compound motor driving pulsed torque load
5.An electric motor with constant output power will have a torque speed characteristic in the form of a
- AStraight line through the origin
- BStraight line parallel to speed axis
- CCircle about the origin
- DRectangular hyperbola
6.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
- ADrop in speed and rise in current
- BRise in speed and drop in current
- CRise in speed and rise in current
- DDrop in speed with current unaltered
7.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
- A49%
- B51%
- C50%
- D70%
8.When the torque of a dc series motor is tripled, the power approximately increases by
- A33%
- B50%
- C75%
- D150%
9.When an electric train is moving down a hill, the DC Series motor will operate as a
- ADC Series motor
- BDC Series generator
- CDC Shunt motor
- DDC Shunt generator
10.A dc series motor should not be started on no load because it would
- ANot develop starting torque
- BFail to start without load
- CRun at dangerously high speed
- DDraw more current without producing sufficient torque
11.In case of a dc series motor it is possible to have finite no load speed if a resistance is connected across its
- AField terminals
- BArmature terminal
- CField and armature together
- DIt is always very high at no load
12.DC series motor is best suited for electric traction as
- AIt develops high starting torque
- BIt runs at very high speed at light load
- CIt is cheaper in cost
- DIt consumes less power
13.A dc series motor is running at rated speed without any additional resistance in series. If an additional resistance is placed in series, the speed of motor
- AIncreases
- BDecreases
- CRemains unchanged
- DOscillates around the rated speed
14.A dc series motor is used for an overhauling load, it can work stably if
- AThe armature is shunted by a resistor
- BThe field winding is reversed
- CA resistor is put in series with the machine
- DA diverter is put across the field
15.A dc shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will
- ARemain unchanged
- BIncrease
- CDecrease be zero
- DBe zero
16.A DC Shunt motor may have rising speed torque characteristic due to
- AVery high armature circuit resistance
- BVery high filed circuit resistance
- CVery high demagnetizing armature reaction
- DVery low demagnetizing armature reaction
17.If the speed of a dc motor increase with load torque, then it is a
- ASeries motor
- BPermanent magnet
- CDifferentially compounded motor
- DCumulatively compounded motor
18.A separately excited dc generator is feeding a dc shunt motor. If the load torque on the motor is halved approximately
- AArmature current of both motor and generator are halved
- BArmature current of motor is halved and that of the generator is unaltered
- CArmature current of generator is halved and that of motor is unaltered
- DArmature current of both motor and generator are unaltered
19.In a dc motor, if armature current is increased, keeping field current constant, the torque developed will
- ARemain unchanged
- BDecrease in inverse proportion
- CIncrease proportionately
- DIncrease I proportion to the square of the armature current
20.If the supply voltage to a dc shunt motor is increased by 15%, which of the following will reduced?
- AFull load current
- BFull load speed
- CStarting torque
- DNone of the above