Question is ⇒ In a motor, energy conversion would not have been possible but for the, Options are ⇒ (A) production of opposing back e.m.f. Eb in the armature, (B) input energy from supply, (C) use of commutator, (D) application of Fleming's left-hand rule, (E) , Leave your comments or Download question paper.

Question is ⇒ In a motor, energy conversion would not have been possible but for the, Options are ⇒ (A) production of opposing back e.m.f. Eb in the armature, (B) input energy from supply, (C) use of commutator, (D) application of Fleming's left-hand rule, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In a motor, energy conversion would not have been possible but for the
A.	production of opposing back e.m.f. Eb in the armature [Correct Answer]
B.	input energy from supply [Wrong Answer]
C.	use of commutator [Wrong Answer]
D.	application of Fleming's left-hand rule [Wrong Answer]
View Answer 6 -5 Explanation:- Answer : A 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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⇒ These days D.C. motors are widely used in
pumping sets
air compressors
electric traction
machine shops

⇒ Which loss in a D.C. generator does not vary with load as well as flux density ?
Copper loss
Eddy current loss
Hysteresis loss
Windage loss

⇒ The total losses in a well designed D.C. generator of 10 kW will be nearly
100 W
500 W
1000 W
1500 W

⇒ In variable speed motor
a stronger commutating field is needed at low speed than at high speed
a weaker commutating field is needed at low speed than at higt speed
same commutating field is needed at low speed than at high speed
none of the above is correct

⇒ Which of the following loss in a D.C. generator is dissipated in the form of heat ?
Mechanical loss
Core loss
Copper loss
All of the above

⇒ Which of the following application requires high starting torque ?
Lathe machine
Centrifugal pump
Locomotive
Air blower

⇒ The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
4.0
2.0
1.0
0.5

⇒ What will happen if supply terminals of D.C. shunt motor are interchanged ?
The direction of rotation will reverse
Motor will stop
Motor will run at speed lower than the normal speed in the same direction
Motor will run at its normal speed in the same direction as it was running

⇒ If conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
less than 50%
60 to 70%
80 to 90%
1

⇒ The main disadvantage of the Ward- Leonard control method is
high initial cost
high maintenance cost
low efficiency at light loads
all of the above

⇒ Which of the following load normally needs starting torque more than the rated torque?
Blowers
Conveyors
Air compressors
Centrifugal pumps

⇒ The operation of electric generators and motors depend on the interaction between magnetic field and
copper conductors
electric field
electric current
commutator

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

⇒ In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
remain unchanged
reduce to one-fourth value
increase four folds
be doubled

⇒ A shearing machine has cyclic load consisting of intermittent light and henry loads. Which of the following D.C. motor will be suitable for this purpose?
Series motor
Shunt motor
Cumulative compound motor
Differential compound motor

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

⇒ 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.

⇒ 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

⇒ Ward-Leonard control is basically a
voltage control method
field divertor method
field control method
armature resistance control method

⇒ A D.C. series motor is that which
has its field winding consisting of thick wire and less turns
has a poor torque
can be started easily without load
has almost constant speed

⇒ Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?
Lenz's law
Faraday's law
Coloumb's law
Fleming's left-hand rule

⇒ Which of the following motors one will choose to drive the rotary compressor ?
D.C. shunt motor
D.C. series motor
Universal motor
Synchronous motor

⇒ The speed of a D.C. shunt motor more than its full-load speed can be obtained by
decreasing the field current
increasing the field current
decreasing the armature current
increasing the armature current

⇒ 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

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

⇒ A series motor is' best suited for driving
machine tools
cranes and hoists
shear and punches
none of the above

⇒ Which losses can be determined by performing the retardation test ?
Friction losses
Eddy current losses
Stray losses
Copper losses

⇒ 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

⇒ If B_max is the maximum flux density, then eddy cu rrent loss will vary as
B_max
(B_max)²
(B_max)^1.2
(B_max)^2.4

⇒ A D.C. shunt motor is rotating in clockwise direction as viewed from one end. The polarity of connection of the armature and field winding are reversed simultaneously. The motor will
rotate in clockwise direction
rotate in anti-clockwise direction
will not rotate at all
gain excessively high speed