.
Graphite
Paper
Mica
Insulating varnish
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Oscillating magnetic field
Pulsating magnetic flux
Relative rotation between field and armature
All above
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Compensating winding in a D.C. machine helps in commutation
 In a D. C. generator interpoles winding is connected in series with the armature winding
Back pitch and front pitch are both odd and approximately equal to the pole pitch
Equalizing bus bars are used with parallel running of D.C. shunt generators
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Using conductor of annealed copper
 Using commutator with large number of segments
Using carbon brushes of superior quality
Using equalizer rings
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Brushes should be of proper grade and size
Brushes should smoothly run in the holders
Smooth, concentric commutator properly undercut
All of the above
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R.p.m. is more than 300
r.p.m. is less than 300
Number of poles is 4
Number of poles is 2
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Insulation failure between two commutator bars
Insulation failure between two turns of a coil
Two of more turns of the same coil getting grounded
All of the above
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Total copper loss and mechanical loss
Armature copper loss and iron loss
Shunt field copper loss and mechanical loss
 Iron loss and mechanical loss
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 Series generator
 Shunt generator
Compound generator
Separately excited generator
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 Is always present
Is always absent
 May be sometimes present
None of the above
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To increase the speed and hence generated e.m.f.
To increase the series flux
So that two similar machines will pass approximately equal currents to the load
Efect of armature reaction To reduce the combined of both machines
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Lenz's law
Ohm's law
 Faraday's law of electromagnetic induction
None of the above
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270 V
267.5 V
265 V
257.4 V
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Increasing its field resistance
Decreasing its field resistance
Increasing its speed
Decreasing its speed
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Slots
 Armature conductors
 Winding elements
Poles
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Number of armature coils
Number of armature coil sides
Number of armature conductors
Number of armature turns
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Lap winding
Wave moving
Duplex winding
 Any of the above
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Constant
Slightly drooping
Slightly rising
Highly drooping
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micaÂ
Copper
Cast ironÂ
carbon
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graphiteÂ
Paper
Mica
insulating varnish
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lie under south pole
Lie under north pole
Lie under interpolar region
are farthest from the poles
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demagnetisation only
Cross magnetisation as well as mag¬netisation
Crossmagnetisation as well as demagnetising
cross magnetisation only
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crossmagnetising
Demagnetising
MagnetisingÂ
none of above
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to avoid sudden loading of the primemover
To avoid mechanicaljerk to the shaft
To avoid burning of switch contacts
all above
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commutatorÂ
Solid connection
Slip ringsÂ
none of above
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speedÂ
Load
Voltage
speed and voltage
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carbonÂ
Soft copper
Hard copperÂ
all of above
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BlvÂ
Blv2
Bl2vÂ
Bl2v2
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4Â
8
16Â
32
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Lap windingÂ
Wave winding
Either of and above
Depends on other features of design
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where low voltage and high currents are involved
Where high voltage and small cur-rents are involved
In both of the above cases
in none of the above cases
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all the four poles are north poles
Alternate poles are north and south
All the four poles are south poles
two north poles follow two south poles
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currentÂ
Voltage
Speed
none of above
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is amenable to better voltage control
Is more stable
Has exciting current independent of load current
has all above features
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direction of induced e.m.f.
Direction of flux
Direction of motion of the conductor if forefinger points in the direction of generated e.m.f.
direction of motion of conductor, if forefinger points along the lines of flux
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ball bearingsÂ
Bush bearings
Magnetic bearmgs
needle bearings
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severe sparking
Rough commutator surface
Imperfect contact
any of the above
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magnetic flux, direction of current flow and resultant force
Magnetic flux, direction of motion and the direction of e.m.f. induced
Magnetic field strength, induced voltage and current
magnetic flux, direction of force and direction of motion of conductor
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double the number of poles
Same as the number of poles
Half the number of poles
two
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Permanent magnet
Electro magnet
Temporary magnet
Any of the above
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Armature
Slip rings
Split rings
Field magnets
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Yoke
Pole cores
Pole shoes
All of the above
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Triangular
Rectangular
Cylindrical
Square
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Field magnet
Armature
Brushes
Yoke
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Ball bearings are used at both driving and non driving ends.
Ball bearings are used at driving end and roller bearings are used at non driving end.
Roller bearings are used at driving end and ball bearings are used at non driving end.
Roller bearings are used at both driving and non driving ends.
Armature core
Commutator
Cooling fan
All of the above
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Series wound generator
Shunt wound generator
Compound wound generator
All of the above
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Mechanical energy into electrical energy
Chemical energy into electrical energy
Electrical energy into Mechanical energy
Electrical energy into chemical energy
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