Question is ⇒ In electric motors carbon brushes are used to, Options are ⇒ (A) provide a path for flow of current, (B) prevent sparking during commutation, (C) prevent overheating of armature windings, (D) brush off carbon deposits on the commutator, (E) , Leave your comments or Download question paper.

Question is ⇒ In electric motors carbon brushes are used to, Options are ⇒ (A) provide a path for flow of current, (B) prevent sparking during commutation, (C) prevent overheating of armature windings, (D) brush off carbon deposits on the commutator, (E) , Leave your comments or Download question paper. Previous question Next question


Q1.	In electric motors carbon brushes are used to
A.	provide a path for flow of current [Correct Answer]
B.	prevent sparking during commutation [Wrong Answer]
C.	prevent overheating of armature windings [Wrong Answer]
D.	brush off carbon deposits on the commutator [Wrong Answer]
View Answer 16 -10 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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⇒ Which D.C. motor is generally preferred for cranes and hoists ?
Series motor
Shunt motor
Cumulatively compounded motor
Differentially compounded motor

⇒ The plugging gives the
zero torque braking
smallest torque braking
highest torque braking
none of the above

⇒ 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
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⇒ What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
The motor will stop
The motor will continue to run
The armature may burn
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⇒ Which of the following motor has high starting torque ?
Synchronous motor
A.C. series motor
D.C. series motor
Induction motor

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field flux
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none of the above

⇒ Which of the following methods of braking is used in rolling mills ?
Dynamic braking
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⇒ Differentially compound D.C. motors can find applications requiring
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⇒ Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?
Series motor
Shunt motor
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Differentially compounded motor

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Ward-leonard control
Armature current resistance control
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the speed of the motor
the voltage across the terminals
none of the above

⇒ During rheostatic braking the braking torque is proportional to
speed
(speed)²
(speed)^-1
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a resistance is connected in series with armature
a resistance is connected parallel to the armature
armature is temporarily open circuited
a high value resistor is connected across the field winding

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

⇒ The speed of a D.C. shunt motor can be increased by
increasing the resistance in armature circuit
increasing the resistance in field circuit
reducing the resistance in the field circuit
reducing the resistance in the armature circuit

⇒ If Ia be the armature current, then speed of a D.C. shunt motor is
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proportional to Ia
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⇒ Sparking at the commutator of a D.C. motor may result in
damage to commutator segments
damage to commutator insulation
increased power consumption
all of the above

⇒ If the field of a D.C. shunt motor gets opened while motor is running
the speed of motor will be reduced
the armature current will reduce
the motor will attain dangerously high speed
the motor will continue to run at constant speed

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a highly resistive circuit
a low resistance circuit
a capacitive circuit
none of the above

⇒ 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
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⇒ In hazardous area of gassy mines, material transportation is done by vehicles powered by
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batteries

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machine tools

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⇒ If t be the thickness of the laminations, then eddy current loss in a generator. will vary as
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cranes and hoists
shear and punches
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⇒ Which D.C. motor Will have least percentage increase of input current for the same percentage increase in the torque?
Shunt motor
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Cumulative compound motor
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