Which of the following basically determines the speed of a dc series motor?
AField excitation
BArmature resistance
CSupply voltage
DLoad carried
Electrical Engineering · Question Bank
DC Motors
218 of 285 questions match · page 3 of 11. Answer in your head first, then check the solution.
Which of the following is used to determine the direction of rotation in a dc motor?
AFleming’s left hand rule
BFaraday’s law
CLenz’ law
DFleming’s right hand rule
What will happen if the field of a shunt motor is suddenly open circuited?
AThe motor will quickly stop from running
BThe speed of the motor will decrease a little
CThe speed of the motor will become so high
DThe motor will continue to run at same speed
In starting a differential compound dc motor, the series field winding must be short circuited first. Why?
ATo prevent the circuit breaker to trip due to large starting current
BTo prevent the motor from starting in the wrong direction
CTo prevent the motor to start at high speed
DTo reduce the losses of the motor at starting
Which one is a common cause why dc motors will overheat?
AOverloads
BOver voltage supply
CLoose parts
DRough commutator segments
An electric train employing a dc series motor is running at a fixed speed when a sudden slight drop in the supply voltage. What will happen?
ASpeed will decrease and current will increase
BSpeed will increase and current will decrease
CBoth speed and current will increase
DSpeed will decrease but the current will remain the same
Why is the air gap between field poles and armature core of a dc motor be kept as small as possible?
ATo decrease the eddy current loss
BTo get a stronger magnetic field
CTo improve the air circulation in the core
DTo achieve a stable speed
As compared to shunt and compound motors, the series motor has the highest starting torque for which of the following reasons?
AIt has a stronger field at start
BIt has fewer series turns at start
CIt has a larger armature current at start
DIt has a lower armature current at start
What is the back emf of the motor when the mechanical power developed by a dc motor is maximum?
AEqual to zero
BEqual to the applied voltage
CEqual to half the applied voltage
DIt is approaching the value of the applied voltage.
DC shunt motor speed is increased by which of the following?
AShifting brushes
BBy cutting-in rheostat resistance in the shunt field
CBy cutting-out rheostat resistance in the shunt field
DNone of these
If a motor frame is found to be excessively hot, which of the following is not likely the cause?
AExcessive loading
BInadequate internal ventilation
CVery high ambient temperature
DFaulty starter
What will you do if the speed of a dc shunt motor should be increase more than the full load speed?
AIncrease the armature current
BIncrease the field current
CDecrease the field current
DDecrease the armature current.
What is the purpose of a “diverter” in a dc series motor?
ATo control the armature current
BTo control the line current
CTo control the speed
DTo control the losses of the motor
What is the reason why a dc shunt motor does not operate on ac supply?
AIts armature resistance is low
BIts field circuit has high resistance
CIts field circuit has high inductance
DDue to reversal of polarity.
Which of the following dc motors is suitable to drive punch press?
ACumulative compound motors
BDifferential compound motors
CSeries motors
DShunt motors
What type of current is flowing in the armature conductors of a dc motor?
AAlternating current
BDirect current
CA non-sinusoidal current
DA full-wave rectified current
Which one is true about the back emf of a dc motor?
AIt aids the supply voltage
BIt opposes the supply voltage
CIt aids both the field and supply voltages
DIt opposes both the field and supply voltages
If the polarity of a dc supply is reversed, what will happen to the self-excited dc motors connected to these supply lines?
AThe motors will stop
BThe motors will increase speed
CThe motors will rotate in reverse direction
DThe motors will rotate in the same direction
What will happen if the field flux of a dc motor will approach zero?
AThe motor will stop quickly
BThe speed will become dangerously high
CThe motor will burn because the current will become very high
DThe counter emf of the motor will go up quickly to a high value
Which of the following is not necessarily the advantage of dc motors over ac motors?
AHigh starting torque
BWide speed range
CLow cost
DBetter speed control
More Electrical Engineering topics
- 1-Phase AC Circuits115
- 1P AC Circuits161
- 3-Phase AC Circuits83
- 3-Phase Induction Motors46
- 3P AC Circuits71
- 3P Induction Motors135
- Alternators157
- Basic Principles30
- circuits301
- Communications408
- Converters & Rectifiers59
- DC Circuits52
- DC Electric Circuits84
- DC Generators196
- Electrical Power Plant195
- Electrical Transients72
- Electromagnetic Induction68
- Electromagnetics350
- Electronics433
- Electrostatics100
- Energy Conversion357
- Engineering Materials117
- Faults106
- Fundamentals of Electricity141
- Illumination143
- Industrial Electronics205
- Instrumentation224
- Instruments & Measurements94
- Instruments and Measurements33
- Laws113
- Magnetic Circuits84
- Magnetism24
- Miscellaneous83
- Miscellaneous Topics33
- Network Laws & Theorems9
- Non-Sinusoidal Waveforms13
- Philippine Electrical Code33
- Power Factor Correction38
- Power Factor Corrections23
- Power Systems32
- Synchronous Motors112
- Transformers258
- Transmission Lines168