300 Important DC Motor MCQ Questions & Answers with Explanation | PDF Free Download
1.In the block diagram of a separately excited dc motor how does the armature induced emf appear as?
- APositive feedback
- BNegative feedback
- CDisturbance input
- DOutput
2.In a dc motor energy conversion would not have been possible but for
- AInput energy from the supply
- BProduction of back emf in the armature
- CUse of commutator
- DRotation of the machine
3.The current drawn by a 120 V dc motor with back emf of 110 V and armature resistance of 0.4 ohm is
- A4 A
- B25 A
- C275 A
- D300 A
4.A 220 V dc machine has an armature resistance of 1 ohm. If the full load current is 20 A , the difference of induced voltage, when the machine is running as a motor and generator is
- A20 V
- B0 V
- C40 V
- D60 V
5.The current drawn by a 220 V dc motor of armature resistance 0.5 ohm and back emf 200V is
- A40 A
- B44 A
- C400 A
- D440 A
6.With the increase in speed of a dc motor
- ABoth back emf as well as line current increase
- BBoth back emf as well as line current fall
- CBack emf increases but line current falls
- DBack emf falls and line current increases
7.If the back in a dc motor vanishes suddenly, the motor will
- AStart hunting
- BBurn
- CRun at very high speed
- DRun at very slow speed
8.The output power of any electrical motor is taken from the
- AArmature
- BField
- CCoupling mounted on the shaft
- DMotor frame
9.The armature shaft must be able to withstand
- AAny unbalanced magnetic pull on the armature core
- BTwisting strains due to transmission of torque
- CBending moment due to weight of the armature and commutator
- DAll of the above
10.The output indicated on the name plate of any motor is always the
- AGross power
- BPower drawn in kVA
- CPower drawn in kW
- DOutput power at the shaft
11.A thicker wire is used in dc series motor filed winding than that in a dc shunt motor.
- ATo create more flux
- BTo reduce resistance
- CTo carry large load current
- DBoth (b) and (c)
12.In case of a conductively compensated dc series motor, the compensating winding is provided
- AIn series with the armature winding
- BIn parallel with the armature winding
- CIn parallel with the field winding
- DAs a separate unit
13.The dc compounded motors are generally
- ALevel compounded
- BCumulative compounded
- CDifferential compounded
- DNone of these
14.In a dc compound motor, the filed regulator is provided to
- AControl the flux
- BLimit the armature current
- CDemagnetize filed partially
- DNone Of the above
15.The direction of rotation of a dc motor can be determined by
- AFleming?s right-hand rule
- BFleming left hand rule
- CLenz?s law
- DAmpere law
16.The direction of rotation of a dc shunt motor can be reversed by interchanging
- AThe supply terminals
- BThe filed terminals only
- CThe armature terminals only
- DEither field or armature terminals
17.When the supply terminals of a dc shunt motor are interchanged
- AThe motor will stop
- BThe motor will run at its normal speed in the same direction as before
- CThe direction of rotation will reverse
- DThe motor will run much faster in the same direction
18.The direction of rotation of a dc series motor can be reversed
- ABy interchanging supply terminals
- BBy interchanging field terminals
- CEither by interchanging supply terminals or by interchanging field terminals
- DBy interchanging supply terminals as well as field terminals
19.The speed of a dc motor is
- Adirectly proportional to back emf and flux
- Bdirectly proportional to it back emf and inversely proportional to flux
- Cinversely proportional to both back emf and flux
- Ddirectly proportional to flux and inversely proportional to back emf
20.If the load current and flux of a dc motor are held constant and voltage applied across it armature is increased by 54%, the speed of the motor will
- Aincrease by 5%
- Breduce by 5%
- Cremain un-alternated
- Ddepends on other factors