In a dc motor, the ratio \(E_b/V\) is an indication of which of the following?
ASpeed regulation
BEfficiency
CRatio of starting torque to rated torque
DPower losses
Electrical Engineering · Question Bank
DC Motors
285 questions · page 8 of 15. Answer in your head first, then check the solution.
A dc shunt motor is running with a certain load. What is the effect if an external resistance is added in the field circuit?
AThe motor will stop running
BThe motor speed will decrease
CThe motor speed will increase
DThe armature current will be reduced
Which of the following dc motor parts can sustain the maximum high temperature rise?
ACommutator
BSlip rings
CArmature windings
DField windings
What is the reason why dc motors are still used in industrial applications up to today?
AIt provides fine speed controls
BIt has a cheaper cost than ac motors
CIt has a simple and rugged construction
DIt has a higher efficiency than ac motors
When a dc motor is overloaded, the motor is in danger because of which of the following?
ACommutator segments are getting overheated
BArmature windings are getting overheated
CMotor bearings are getting overheated
DStarting resistance are getting overheated
What type of dc motors are suitable to drive elevators?
ASeries motors
BShunt motors
CCumulative compound motors
DDifferential compound motors
What will happen to the speed of a shunt motor if the load is removed?
AIt will slow down
BIt will stop
CIt will speed up slightly
DIt will remain at the same speed
In a dc motor, which of the following is the reason why shaft torque is less than armature torque?
AStray losses
BEddy current losses
CHysteresis losses
DAll of these
What is the main disadvantage of the Hopkinson's test for finding the efficiency of shunt motors?
AIt needs one motor and one generator
BIt requires two identical shunt machines
CIt requires full load power
DIt ignores any change in the iron loss
Which of the following dc motors has the least drop in speed from no load to full load?
AShunt motors
BSeries motors
CCumulative compound motors
DDifferential compound motors
The iron losses of a dc motor is dependent on which of the following?
ASpeed only
BFlux only
CLoad carried
DBoth speed and flux
What is the purpose of laminating the armature core of a dc motor?
ATo reduce the eddy current loss
BTo help ventilate the core
CTo reduce the armature copper loss
DTo prevent the core from being short circuited
Which of the following characteristics is the deciding factor in the selection of a dc motor for a particular application?
ASupply voltage - armature current
BTorque - armature current
CSpeed - torque
DTorque - power output
At light loads, a cumulative compound motor does not run dangerously on high speed because of this winding. Which one?
AArmature windings
BSeries field windings
CCompensating windings
DShunt field windings
When the load of a dc shunt motor is increased, what will happen to its speed?
AIt will remain the same
BIt will reduce slightly
CIt will increase proportionately
DIt will decrease in proportion to the square of the current
What will you do to reverse the rotation of a dc motor?
AInterchange the field terminals only
BInterchange the armature terminals only
CInterchange both the armature and field terminals simultaneously
DEither A or
Which of the following dc motors would be suitable for drives requiring high starting torque but only fairly constant speed such as crushers?
ASeries motor
BShunt motor
CCompound motor
DAny of these
What is common to both Hopkinson’s and Field tests in dc motors?
ABoth are regenerative tests
BBoth use negligible power
CBoth need two electrically coupled series motors
DBoth need two similar mechanically coupled motors
Which one is true about the back emf of a dc motor?
AThe counter emf helps in energy conversion
BThe counter emf regulates its armature voltage
CThe counter emf of a dc motor aids the applied voltage
DThe counter emf of a dc motor exceeds the supply voltage
What will happen if the load is suddenly released from a series motor?
AIt will speed up
BIt will slow down
CIt will stop
DIt will continue to operate at the same speed
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