DC Machine MCQ's (Multiple choice questions)

 

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1. where is the field winding placed in DC machine?

A) stator
B) Rotor
C) Stator as well as rotor
D) None of the above

ANSWER= (A) Stator
Explain:- In DC machine field winding is mounted on stator and in AC machine field winding is placed on rotor.
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2. In dc machine ,the field flux axis and armature flux axis are respectively placed along

A) direct axis and idirect axis
B) direct axis and inerpolar axis
C) quadrature axis and direct axis
D) quadrature axis and interpolar axis

ANSWER= (B) direct axis and inerpolar axis

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3. the armature core of dc machine is made up of?

A) laminations
B) solid material
C) forged material
D) Aluminium material

ANSWER= (A) laminations
Explain:- the armature core of dc machine is made up oflaminationsso the circular path of eddy currentis terminated.
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4.the commutator of dc machine is made up of?

A) aluminium
B) copper
C) brass
D) nikel

ANSWER= (B) copper
Explain:- the commutator of dc machine is mader up of hard drawn copper.
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5.Shunt motor is used for?

A) line shafting
B) variable speed
C) constant speed
D) all of the abvove

ANSWER= (C) constant speed
Explain:- in case of DC shunt motor flux is practically constantas the field is parallel to the aramature.if the load is increased then the speed of the motor will remain almost constant.
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6. Which of the following winding are necessary in case of all dc machine?

A) closed winding
B) lap winding
C) wave winding
D) open type winding

ANSWER= (A) closed winding
Explain:- In case of all dc machines we use closed winding.lap and wave windings are used according to the requirement of voltage and current level.but remember always dc machine windings are never short pitched.
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7. No load saturation chracterstics are plotted between?

A) no load voltage and field current
B) no load voltage and armature current
C) short circuit current and field current
D) short circuit current and armature current

ANSWER= (A) no load voltage and field current
Explain:- This curve is plotted between no load armature generated voltage with field or exciting current.
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8. For dc machine shunt resistance and armature resistance value are respectively

A) high,low
B) low,high
C) low,low
D) high,high

ANSWER= (A) high,low
Explain:- The value of armature resistance is very low ans shunt resistance is very high.series resistance extreamly low because power deliver by the dc machine Ia.Ia should be high to get maximum power
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9. The effact of _____ on main field flux is armature reaction.

A) armature mmf
B) armature current
C) armature flux
D) none

ANSWER= (C) armature flux
Explaination:- the effact of armature flux on main field flux is called armature reaction.
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10. cross magnetisation effact results which of the following?

A) commutation
B) reduction in the main flux
C) reduce the terminal voltage
D) none

ANSWER= (A) commutation
Explaination:- cross magnetisation is the effact of armature reaction.
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11.Magnetic flux usually flow through a minimum reluctance path.

A) True
B) FAlse

ANSWER= (A) True
Explaination:- Magnetic flux always flow through a minimum reluctance path.
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12. iron loss in dc machine are indipendent of variation in ?

A) speed
B) load
C) voltage
D) speed and voltage

ANSWER= (A) load
Explaination:- iron losses are remain same at any kind of load they are indipendent of load.
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13.The critical field resistance is defined as the maximum field circuit resistance (for given speed) with which the shunt generator would excite and above which voltage build up not possible.

A) True
B) False

ANSWER= (A) True

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14.In dc generator the critical resistance can be increased by ?

A) increasing its field resistance
B) decreasing its field resistance
C) increasing its speed
D) none of the above

ANSWER= (A) increasing its speed
Explaination:- critical resistance can be increased by increasing its speed.
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15.frequent starting and stopping of electric motor needed?

A) grinding mills
B) papper mills
C) air conditioners
D) Lifts and hoist

ANSWER= (D) Lifts and hoist
Explaination:- frequent starting and stopping of electric motor needed for lifts and hoist where motor starting and stopping are very frequent.
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16.which dc motor is more preferred for elevators,shears and punches?

A) shunt motor
B) series motor
C) defferential compound motor
D) cumulative compound motor

ANSWER= (cumulative compound motor)
Explaination:- cumulative wound dc motor gives high starting torque like a series motor and provide good speed regulation.
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17.DC series motor is extensively used for electric traction, railways,tramways and trolles.

A) True
B) False

ANSWER= (A) True

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18.pole shoe of dc motor is laminated for the purpose of ?

A) Decreasing hysteresis loss
B) decreasing eddy current loss
C) both of the above
D) none of the above

ANSWER= (A) decreasing eddy current loss
Explaination:- pole shoe of dc motor is laminated for the purpose of decreasing eddy current loss.
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19.in dc generator on no load , the air gap flux distribution in space is ?

A) sinusoidal
B) Triangular
C) pulsating
D) Flat topped

ANSWER= (D) Flat topped
Explaination:-in dc generator on no load , the air gap flux distribution in space is FLAT TOPPED.
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20.Carbon brushes are used in a electric motor to ?

A) Provide a path for flow of current
B) prevent sparking during commutation
C) both
D) none

ANSWER= (A) both
Explaination:- Carbon brushes are used in a electric motor to Provide a path for flow of current and prevent sparking during commutation.
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