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
Electrical Engineering · Question Bank
DC Motors
208 of 285 questions match · page 5 of 11. Answer in your head first, then check the solution.
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
When load is removed which dc motors will run at the highest speed?
ASeries motors
BShunt motors
CCumulative compound motors
DDifferential compound motors
What is the purpose of a “starter” in a dc motor?
ATo start the motor easily and quickly
BTo control the speed of the motor at start
CTo limit the starting current to a safe value
DTo keep the operator safe from starting currents
What will happen to the back emf of a dc motor if its speed will increase?
AIt will increase
BIt will decrease
CIt will remain constant
DIt will increase or decrease depending on the type of dc motor
DC shunt motors are used in which of the following applications?
AHigh no load speed
BHigh starting torque
CPractically constant speed
DVariable speed over a wide load range
What will happen to the speed of a dc series motor when the load is increased?
AIt will decrease
BIt will increase
CIt will remain the same
DEither A or B only
Which of the following tests can be used to determine the no load losses in a dc motor?
ARunning down test
BField test
CBrake test
DSwinburne’s test
Under constant load conditions, the speed of a dc motor is affected by which of the following?
ABack emf
BFlux
CArmature current
DBoth B and C
What is the usual speed of a dc series motor at no load?
AZero
BVery high
CAround 500 to 1000 rpm
DAround 3000 to 3600 rpm
How do you call the variable resistor shunting the field of a series dc motor?
AVoltage regulator
BPotential divider
CField diverter
DArmature diverter
The yoke of a dc motor is normally made from which of the following materials?
AMica
BSteel
CCopper
DIron
What will happen to a dc series motor when connected across an ac supply?
AIt will develop a torque in the same direction
BIt will not develop any torque
CIt will draw dangerously high current
DIt will develop a pulsating torque
As compared to shunt and compound motors, a series motor has the highest starting torque due to which of the following?
AWeak series field at start
BLarge armature current at start
CLower armature current at start
DStronger series field at start
What is the function of the commutator in a dc motor?
AIt will prevent sparking between brushes and armature windings
BIt will convert alternating current to direct current
CIt will convert direct current to alternating current
DIt will reduce the friction and windage losses
A “brake test” is applicable only in which of the following types of dc motors?
ASmall horsepower motors
BHigh speed motors
CSeparately-excited motors
DOpen frame type motors
Which of the following is used to vary the speed of a dc motor?
AVary its flux per pole
BVary the resistance of its armature circuit
CVary the applied voltage
DAll of these
Which of the following dc motors has the best speed regulation?
ASeries motor
BShunt motor
CDifferential compound motor
DCumulative compound motor
Which one limits the maximum torque on a dc motor?
AHeating
BSpeed
CCommutation
DMechanical loss
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