Most single-phase motors have how many poles?
A2 poles
B6 poles
C4 poles
D8 poles
Electrical Engineering · Question Bank
DC Motors
208 of 285 questions match · page 2 of 11. Answer in your head first, then check the solution.
Most of the troubles in single phase induction motors are traceable in which of the following?
ARotor bars
BMain winding
CStarting switch
DShaft bearings
Single phase series motor can operate using what type of voltage?
AAC only
BDC only
CBoth AC and DC voltages
DAny type of voltages
Which motor is generally employed in a washing machine?
AHysteresis motor
BShaded pole motor
CSeries ac motor
DResistance split phase motor
Which of the following application a reluctance motor is preferred?
ASignalling and timing devices
BElectrical shavers
CLifts and hoists
DRefrigerators
Which one is the least expensive fractional horsepower motor?
ASplit-phase motor
BShaded pole motor
CCapacitor start motor
DAC series motor
For the same rating, which dc motor has the lowest starting torque?
AShunt motors
BSeries motors
CLong-shunt compound motors
DShort-shunt compound motors
The shaft torque of dc motor is less than the armature torque due to this loss. Which one?
ACopper loss
BIron loss
CMechanical loss
DRotational loss
Which of the following is the most common method used in controlling the speed of a dc motor?
AVary the supply voltage
BVary the field strength
CVary the number of field pole
DVary the armature circuit resistance
What is the rotating part of a dc motor?
APole
BStator
CArmature
DCarbon brush
Which of the following basically determines the speed of a dc series motor?
AField excitation
BArmature resistance
CSupply voltage
DLoad carried
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
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