Question is ⇒ Which of the following loss of D.C. motor decreases with increase in load ?, Options are ⇒ (A) Friction and windage loss, (B) Core loss, (C) Brush contact loss, (D) none of the above, (E) , Leave your comments or Download question paper.

Question is ⇒ Which of the following loss of D.C. motor decreases with increase in load ?, Options are ⇒ (A) Friction and windage loss, (B) Core loss, (C) Brush contact loss, (D) none of the above, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	Which of the following loss of D.C. motor decreases with increase in load ?
A.	Friction and windage loss [Wrong Answer]
B.	Core loss [Wrong Answer]
C.	Brush contact loss [Wrong Answer]
D.	none of the above [Correct Answer]
View Answer 9 -16 Explanation:- Answer : D Discuss it below : !! OOPS Login [Click here] is required to post your answer/result Help other students, write article, leave your comments

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⇒ The armature shaft of a D.C. motor must be able to withstand
any unbalanced magnetic pull on the armature core
twisting strains due to transmission of torque
bending moment due to the weight of the armature and commutator
all of the above

⇒ The condition for maximum power in case of D.C. motor is
back e.m.f. = 2 x supply voltage
back e.m.f. = 1/2 x supply voltage
supply voltage = 1/2 x back e.m.f.
supply voltage = back e.m.f.

⇒ Which of the following can be used for controlling the speed of a D.C. motor ?
Thermistor
Transistor
Thyratron
Thyristor

⇒ Which of the following methods gives the greatest breaking torque ?
Regenerative braking
Plugging
Rheostatic braking
None of the above.

⇒ Which of the following motors is usually used in house-hold refrigerators ?
D.C. shunt motor
D.C. series motor
Single phase induction motor (split phase start or induction run motor)
Reluctance motor

⇒ D.C. series machine has field consisting of
many number of turns of thick wire
many number of turns of thin wire
few number of turns of thick wire
few number of turns of thin wire

⇒ Which of the following loss in a D.C. generator varies significantly with the load current ?
Field copper loss
Windage loss
Armature copper loss
None of the above

⇒ Following motor is used where high starting torque and wide speed range control is required.
Single phase capacitor start
Induction motor
Synchronous motor
D.C. motor

⇒ D.C. series motors are used
where load is constant
where load changes frequently
where constant operating speed is needed
in none of the above situations.

⇒ In a D.C. generator all of the following could be the effects of iron losses except
Loss of efficiency
Excessive heating of core
Increase in terminal voltage
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⇒ For the same H.P. rating and full load speed, following motor has poor starting torque
shunt
series
differentially compounded
cumulatively compounded

⇒ In which of the following tests only one motor is required ?
Brake test
Hopkinson's test
Field's test
Swinburne's test

⇒ Which of the following method of speed control, of D.C. machine will offer minimum efficiency ?
Voltage control method
Field control method
Armature control method
All above methods

⇒ Why are the D.C. motors preferred for traction applications ?
Torque and speed are inversely proportional to armature current
Torque is proportional to armature current
Torque is proportional to square root of armature current
The speed is inversely proportional to the torque and the torque is proportional to square of armature current

⇒ Which of the following statement is incorrect ? If a starter is not used with large D.C. motor, it will draw a starting current which
will produce very low starting torque
will produce excessive line voltage drop
will damage the cOmmutator
is many times its full-load current

⇒ Starters are used with D.C. motors because
these motors have high starting torque
these motors are not self-starting
back e.m.f. of these motors is zero initially
to restrict armature current as there is no back e.m.f. while starting

⇒ While starting a differential compound motor, it is best to short the series field in order to avoid
excessive starting period
motor starting in wrong direction
tripping of the circuit breaker
large in rush of current

⇒ The condition for maximum efficiency for a D.C. generator is
eddy current losses = stray losses
hysteresis losses = eddy current losses
copper losses = 0
variable losses = constant losses

⇒ Which method of braking is generally used in elevators ?
Plugging
Regenerative braking
Rheostatic braking
None of the above

⇒ Which of the following can be used to control the speed of a D.C. motor ?
Thermistor
Thyristor
Thyratron
Transistor

⇒ If t be the thickness of the laminations, then eddy current loss in a generator. will vary as
¹/_t
¹/_t²
t
t²

⇒ Which motor should not be started on no-load ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor

⇒ Usually wide and sensitive speed control is desired in case of
centrifugal pumps
elevators
steel rolling mills
colliery winders

⇒ The speed of a D.C. series motor is
proportional to the armature current
proportional to the square of the armature current
proportional to field current
inversely proportional to the armature current

⇒ In a D.C. motor constant torque is produced due to
rotor laminations
end-plates
pole shoes
commutator

⇒ No-load speed of which of the following motor will be highest ?
Shunt motor
Series motor
Cumulative compound motor
Differentiate compound motor

⇒ Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
D.C. series motor
D.C. shunt motor
induction motor
all of above motors

⇒ D.C. generators are installed near the load centres to reduce
iron losses
line losses
sparking
corona losses

⇒ If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
Starting torque
Operating speed
Full-load current
All of the above

⇒ VVhat is the effect produced by the electric current in an electric motor ?
Heating effect only
Magnetic effect only
Heating as well as magnetic effect
Heating as well as chemical effect