DC Machines - EEES.IN

#1. A DC generator works on the principle of….?

mutual infuction

faraday's laws of electromagnetic infuction

lenz's law

flemmings law

incorrect

#2. The process by which an emf induced in a DC generator is called…….?

Chemical

Thermal

Static

Dynamic

incorrect

#3. The direction of dynamically induced emf in DC generator can be identified by rule of…..?

flemmings right hand

flemmings left hand

right hand grip

right hand palm

incorrect

#4. The yoke of a dc machine made of….?

silicon steel

aluminium

cast steel

soft iron

#5. The armature of dc machine is made by….?

cast iron

cast steel

silicon steel

Alnico

#6. The thickness of laminations of armature core varies from….?

1 mm to 0.25 mm

2mm to 0.6 mm

1 mm to 2.5 mm

0.3 mm to 0.9 mm

armature core laminations approximately 0.5 mm thick

#7. The armature core is laminated to minimise the….?

hysteresis loss

eddy current loss

size

copper loss

#8. Carbon brushes are used in dc machine because of….?

negative temperature coefficient and lubricates the commutator

positive temperature coefficient

carbon is weightless and cheap

none of the above

incorrect

welding generator used metal graphite brushes.

#9. The material used for commutator is….?

silicon steel

aluminium

hard drawn copper

silver

incorrect

#10. In small capacity dc machines the yoke is made up of….?

aluminium

bronze

cast iron

cast steel

#11. The material used for split ring is….?

silver

aluminium

gold

copper

#12. The number of parallel path in the wave winding of a dc machine is….?

4

3

2

1

#13. The number of parallel path in a lap winding dc machine is….?

2

number of poles

4

number of pairs of poles

#14. A lap winding is made in a machine for….?

more current, more voltave

less current less voltage

more current, less voltage

less current, more voltage

#15. High voltage dc machines use which winding?

lap

wave

either lap or wave

none of the above

#16. In a 4 pole lap wound dc machine the resistance of one conductor is 0.2 ohm of 64 conductors.calculate the armature resistance?

0.9

0.8

0.4

0.3

incorrect

conductors/parallel path= 64/4=16

resistance/parallel path=16×0.2=3.2ohm

total armature resistance for 4 parallel path= 3.2/4=0.8 ohm

#17. Slot wedges in a dc machine are made of….?

copper

silicon steel

cast iron

cast steel

#18. An exciter for a generator is ….?

series motor

series generator

shunt motor

shunt generator

#19. The commutator of a dc generator act as….?

a load

an amplifier

an inverter

a rectifier

#20. Flemmings right hand rule applicable to….?

alternator

transformer

dc generator

dc motor

#21. A dc series motor is most suitable for….?

lathes

cranes

pump

punch presses

#22. In which type of DC motor, two point starter is used?

series

shunt

long shunt compound

short shunt compound

#23. Which type of DC generator is used for battery charging?

series generator

shunt generator

cumulative compound generator

differential compound generator

#24. Two dc series motors are connected in series to produce a torque T. now if the motors are connected in parallel, the torque produced will be….?

T

T/2

T/4

2T

#25. For traction which motor is used…..?

DC series

DC shunt

synchronous

slip ring induction

#26. Which motor has widest variety of methods of speed control?

synchronous motor

induction motor

dc series motor

dc shunt motor

#27. Interpoles are used for…..?

increasing emf

increasing the speed of the motor

reducing sparking at the commutator

decreasing speed of the motor

#28. No load speed of dc series motor is……?

very low

very high

medium

low

#29. The condition for a maximum power output from a dc motor is Eb=…..?

V

0

V/2

2V

#30. In swinburns method of testing dc machines. the shunt motor is run as a…..?

motor at full load

generator at full load

motor at no load at rated speed

generator at no load at rated speed

#31. Poles of dc machine are often laminated to…..?

reduce iron weight

reduce pulsation loss

reduce armature reaction

reduce heat loss

#32. The armature of dc machine is made of silicon steel laminations to ….?

reduce hysteresis loss

reduce eddy current loss

reduce corona loss

reduce both hysteresis and eddy current loss

#33. The teeth of the armature of dc machine are skewed is to reduce…….?

hysteresis loss

copper loss

corona loss

vibrations

#34. The commutator of dc motor serves the purpose of…..?

changing ac to dc

changing dc into ac

reduce friction

reduce sparking

#35. In dc machines armature windings are placed on the rotor because of the necessity for….?

development of torque

electromechanical energy conversion

generation of voltage

commutation

#36. A lap wound dc machine has 800 conductors and 12 poles. The voltage induced per conductor is 2V. The machine generates a voltage of…..?

100 V

200V

400V

800V

#37. Th brushes of a dc machine should be physically placed on the….?

armature in the polar axis

armature in the inter polar axis

commutator in the polar axis

commutator in the inter polar axis

#38. The highest speed attained by dc shunt motor is….?

much higher than no load speed

much lower than no load speed

equal to no load sped

equal to full load speed

#39. The direction of rotation of shunt motor can be reversed by inter changing….?

the armature terminal only

the field terminal

the supply terminal

either field or armature terminal

#40. Which of the following motor can work satisfactorily on both AC & DC?

series motor

shunt motor

induction motor

synchronous motor

#41. Eddy current of the ferromagnetic core is propotional to…..?

frequency

square of frequency

square root of frequency

reciprocal of frequency

#42. Which motor should not be used for centrifugal pump?

series

shunt

cumulative compound

differential compound

#43. The speed of the DC motorcan be controlled by….?

its flux

armature resistance

applied voltage

all the above

#44. The core losses in a dc machine occures in…..?

armature only

pole faces only

both the armature & pol faces

yoke only

#45. The speed of dc series motor at no load is….?

zero

infinity

1500rpm

3000rpm

#46. DC shunt motor is a …..?

high speed motor

constant speed motor

variable speed motor

#47. DC shunt motor is a …..?

high speed motor

constant speed motor

variable speed motor

#48. If a dc motor is connected to ac supply, it will….?

run at normal speed

not run

run at lower speed

burn due to heat produced in field by eddy currents

#49. Four point starter can be used for…..?

series motor

shunt motor

compound motor

both shunt motor & compound motor

#50. Which of the following motor has poorest speed regulation?

series motor

shunt motor

differential compound motor

cumulative compound motor

#51. The magnitude of the back emf depends on….?

flux per pole

speed of motor

number of parallel path in armature

all the above

#52. A shunt motor can be started with….?

two point starter

three point starter

star delta starter

autotransformer starter

#53. Compensating winding of dc motor is connected in……?

series with field

series with armature

parallel with armature

series parallel with armature

#54. If the field of the shunt motor is opened….?

the motor will stop

it will continue to run at its rated speed

the speed of the motor will become very high

speed will decrease

#55. A DOL starter is used for starting motors…?

upto 5 Hp

upto 10 Hp

upto 30 Hp

upto 60 Hp

#56. DC shunt motor is used for driving….?

machine tools

lathes

centrifugal pumps

all the above

#57. The commutator in a dc machine acts as….?

mechanical inverter

mechanical rectifier

current controller

either inverter or rectifier

#58. Th purpose of dummy coils in the dc machine is to ….?

eliminate harmonics

eliminate armature reaction

bring mechanical balance of armature

all the above

#59. Functions of interpoles in a dc machine is to….?

reduces losses

improve commutation

improve mechanical balance

reduce heating in the windings

#60. As the load incresed the speed of a shunt motor ……?

remains constant

increased

decreased propotionally

reduced slightly

#61. Commutator segments of dc machine by….?

soft copper

silicon steel

hard drawn copper

hard steel

#62. For a 4 pole dc machine with wave wound armature, the number of brushes required is….?

2

4

6

8

#63. The material used for split rings is…?

gold

copper

aluminium

iron

#64. The split rings are connected to facilitate the output will be….?

flow in same direction

flow in opposite direction

pulsating direction

oscillating current

#65. Armature resistance of a dc machine generally….?

1000 ohm

100 ohm

10 ohm

1 ohm

#66. In a 6 pole simplex lap wound armature, the number of parallel paths are…?

2

4

6

8

#67. As the speed of dc generator increase, the induced voltage will……?

decrease

increase

remains same

drop to zero

#68. Shunt field resistance value for building up voltage should be….?

greater than critical field resistance

less than critical field resistance

infinite its value

none of the above

#69. The current drawn by a dc motor at starting is…?

zero

very low

very high

normal

#70. Plugging of dc machine is normally executed by….?

reversing the field polarity

reversing the armature polarity

reversing both armature & field polarity

connecting resistance series with armature

#71. Nature of induced current in the dc generator is….?

alternating

unidirectional

any of the above

rectified dc

#72. Steinmetz formula is related to….?

copper loss

eddycurrent loss

hysteresis loss

rotational loss

#73. The critical resistance of a dc generator is the resistance of…..?

field

armature

brush

commutator

#74. The wave winding is suitable for……voltage and ……current dc generators?

low, high

high, high

high, low

low, low

#75. In dc machines the armature winding must be….?

open closed one

semi closed one

closed one

any of the above

#76. Which type of dc generators do not need equilizers for satisfactory parallel operation?

under compound

over compound

flat compound

any of the above

#77. Which of the following generator has poorest voltage regulation?

series

shunt

cumulative compound

differential compound

#78. Differential compound generators are suitable for….?

booster

arc welding

battery charging

hoist

#79. Stray losses are….?

copper loss

iron loss

magnetic and mechanical loss

mechanical loss

#80. A compound motor is best suited for driving……?

lathes

traction

reciprocating pump

hoists

#81. For a dc shunt motor, which method is used for wide and very sensitive speed control?

armature voltage control

flux control method

tapped field control

ward leonard method

#82. Which of the motor is not self starting?

universal motor

DC series motor

DC shunt motor

single phase induction motor

#83. If series winding is connected in series with the armature and then the shunt winding is connected parallel to the combination, then such a combination will form which kind of gnerator?

long closed compound generator

short shunt compound generator

long series compound generator

long shunt compound generator

#84. The basic difference in 4 point starter when compared to 3 point starter is…..?

the over current release is connected in supply lines

the holding coil is removed from the shunt field circuit

the holding coil is added from the shunt field circuit

field circuit completed through starting resistance

#85. Which of the following starter used in dc series motor?

two point

three point

four point

five point

#86. Which of the following starter used in dc series motor?

two point

three point

four point

five point

#87. Which of the following starter used in dc series motor?

two point

three point

four point

five point

#88. The number of parallel paths in a simplex 8 pole lap wound armature in a dc generator is…?

16

8

4

2

#89. ……. are loops of electric current induced within conductors by changing magnetic field?

berry currents

electric currents

eddy currents

faulty currents

#90. In a dc motot back emf is directly propotional to…..?

speed

no. of armature conductors

no. of poles

flux

#91. Function of inter poles used in dc machine is to…..?

reduce heating

reduce losses

improve commutation

compensate for air gap variation

#92. The method of speed control of series motor used in electric trains is…..?

armature resistance method

field resistance method

field diverter method

none of these

#93. The dc generator used for arc welding process is……?

cumulatively compound

differentially compound

series

shunt

#94. Interpoles in dc machine used to….?

reduce the effect of cogging

reduce

reduce the effect of armature reaction

none of these

#95. In dc generator armature reaaction is produced by?

armature current

field current

armature & field current

none of these

#96. According to which law, the back emf in DC motor opposes the applied voltage?

faradays law

amperes law

lorentz law

lenz's law

#97. A triplex wave winding have …. parallel path?

2

3

6

9

#98. The open circuit characteristics of a DC generator is also called its ….. characteristics?

magnetic

internal

external

none of these

#99. Which of the following is a loss in DC generator?

iron loss

copper loss

magnetic loss

all the above

#100. The compensating windings are connected in ….. of a DC generator?

series with field winding

parallel with field winding

series with armature winding

parallel with armature winding

#101. Hysteresis loss is proportional to….?

frequency

square of frequency

thickness

square of thickness

#102. The critical field resistance of a shunt generator should be….?

smaller than its shunt field resistance

equal to the shunt field resistance

greater than its shunt field resistance

none of these

#103. The most suitable material for cores of electromagnet is….?

air

aluminium

soft iron

copper

#104. The direction of induced emf can be determined by….?

flemming's left hand rule

flemming's right hand rule

faraday's law

ohms law

#105. Motor used in the household refrigerator is…..?

DC series motor

DC shunt motor

Single phase induction motor

Universal motor

#106. Which motor would you select for vaccum cleaner?

Universal motor

Repulsion motor

Hysterisis motor

Induction motor

#107. The voltage regulation of an over compound dc generator is always…?

zero

positive

negative

unity

#108. The normal value of armature resistance of a dc motor is…?

0.05

0.5

10

100

#109. The speed of dc motor inversely its…?

flux

voltage

frequency

pole

#110. Which test used for find stray losses of DC shunt motor?

Retardation

SC

Hopkinson's

swinburns