DC Generator mcq Question and Answer

DC Generator mcq Question and Answer

1.Torque developed in an electromechanical energy conversion device depends upon

  • Astator field strength and torque angle
  • Bstator field and rotor field strengths
  • Cstator field and rotor field strengths and the torque angle
  • Dstator field strength only
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Correct Answer : (C)

stator field and rotor field strengths and the torque angle

Explanation:

Torque developed in an electromechanical energy conversion device depends upon stator field and rotor field strengths and the torque angle.

2.In electromechanical energy conversion devices (e.g generators and motors) a small air gap is left between the stator and the rotor in order to

  • Areduce the reluctance of the magnetic path
  • Bincrease flux density in the air gap
  • Cpermit mechanical clearance
  • Davoid saturation of field
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Correct Answer : (C)

permit mechanical clearance

Explanation:

In electromechanical energy conversion devices (e.g generators and motors) a small air gap is left between the stator and the rotor in order to permit mechanical clearance.

3.If a current carrying coil is placed in a uniform magnetic field direction of magnetic induction, then

  • Athe net force and torque on the coil are both zero
  • Bthe net force is zero but torque is finite
  • Cthe net force is finite but toque is zero
  • Dthe net force and torque are both finite
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Correct Answer : (A)

the net force and torque on the coil are both zero

Explanation:

If a current carrying coil is placed in a uniform magnetic field direction of magnetic induction, then the net force and torque on the coil are both zero.

4.Reluctance torque in rotating machines is present, when

  • Aair gap is not uniform
  • Breluctance seen by stator mmf varies
  • Creluctance seen by rotor mmf varies
  • Dreluctance seen by the working mmf varies
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Correct Answer : (D)

reluctance seen by the working mmf varies

Explanation:

Reluctance torque in rotating machines is present, when reluctance seen by the working mmf varies.

5.A rotating electrical machine having its self-inductances of both the stator and the stator windings, independent of rotor position will definitely not develop.

  • AStarting torque
  • BSynchronizing torque
  • CHysteresis torque
  • DReluctance torque
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Correct Answer : (B)

Synchronizing torque

Explanation:

6.A circular metallic disc is placed in a vertical magnetic field of constant induction in the downward direction. If the disc is rotated in a horizontal plane, the emf induced will be

  • AZero
  • BConstant independent of disc size
  • CIncreasing radially in the outward direction
  • DDecreasing radially in the outward direction
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Correct Answer : (A)

Zero

Explanation:

7.The emf induced in a conductor rotating in a bipolar field is

  • ADC
  • BAC
  • CDc and ac both
  • DNone of these
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Correct Answer : (B)

AC

Explanation:

The emf induced in a conductor rotating in a bipolar field is AC

8.A conductor is rotating within a magnetic field. At which of the position do the peak voltages occur?

  • AAt right angles to the axis of magnetic field
  • BAlong the axis of the magnetic field
  • CAt 450 angles to the axis of magnetic field
  • DAnywhere
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Correct Answer : (B)

Along the axis of the magnetic field

Explanation:

A conductor is rotating within a magnetic field. Peak voltages occur when the conductor is Along the axis of the magnetic field.

9.EMF induced ina coil rotating in a uniform magnetic field will be maximum when the

  • AFlux linking with the coil is maximum
  • BRate of change of flux linkage is minimum
  • CRate of change of flux linkage is maximum
  • DRate of cutting flux by the coil sides is minimum
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Correct Answer : (C)

Rate of change of flux linkage is maximum

Explanation:

EMF induced ina coil rotating in a uniform magnetic field will be maximum when the Rate of change of flux linkage is maximum.

10.In a dc motor the windage loss is proportional to

  • ASupply voltage
  • BSquare of the supply voltage
  • CSquare of the flux density
  • DSquare of the armature speed
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Correct Answer : (D)

Square of the armature speed

Explanation:

In a dc motor the windage loss is proportional to Square of the armature speed.

11.Which of the following are the variable losses in a rotating machine?

  • ACore loss and mechanical loss
  • BCore loss and stray load loss
  • CCopper lossand core loss
  • DCopper loss and stray load loss
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Correct Answer : (D)

Copper loss and stray load loss

Explanation:

Copper loss and stray load losses are the variable losses in a rotating machine.

12.Stray losses are sum of

  • AIron and mechanical losses
  • BCopper and iron losses
  • CCopper and mechanical losses
  • DNone of these
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Correct Answer : (A)

Iron and mechanical losses

Explanation:

Stray losses are sum of  Iron and mechanical losses.

13.Generally, the no ? load losses of an electrical machine is represented in its equivalent circuit by

  • AParallel resistance with a low value
  • BSeries resistance with a low value
  • CParallel resistance with a high value
  • DSeries resistance with a high value
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Correct Answer : (C)

Parallel resistance with a high value

Explanation:

Generally, the no – load losses of an electrical machine is represented in its equivalent circuit by Parallel resistance with a high value.

14.The principle of dynamically induced emf is utilized in

  • ATransformer
  • BChoke
  • CGenerator
  • DThermocouple
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Correct Answer : (C)

Generator

Explanation:

The principle of dynamically induced emf is utilized in Generator.

15.In a dc machine

  • AThe current and emf in armature conductors are alternating while those at the terminals are unidirectional
  • BThe current and emf in armature conductors are unidirectional while those at the terminals are alternating
  • CThe current and emf in armature conductors and at the terminals are unidirectional
  • DThe emf in armature conductors and at the terminals is alternating while current  there is unidirectional
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Correct Answer : (A)

The current and emf in armature conductors are alternating while those at the terminals are unidirectional

Explanation:

16.Which of the following is not a part of dc machine?

  • AArmature
  • BCommutator
  • CField winding
  • DDamping winding
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Correct Answer : (D)

Damping winding

Explanation:

hints

17.The field coils of a dc generator are usually made of

  • AMic
  • BCopper
  • CCast iron
  • DCarbon
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Correct Answer : (B)

Copper

Explanation:

The field coils of a dc generator are usually made of Copper because it has good electrical conductivity as well as good thermal conductivity. 

18.Laminated yoke in dc motor can reduce

  • ASpeed regulation
  • BIron loss
  • CTemperature rise
  • DSparking non load
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Correct Answer : (B)

Iron loss

Explanation:

Laminated yoke in dc motor can reduce Iron loss.

19.Pole shoe of a dc machine is laminated for the purpose of 

  • ADecreasing hysteresis loss
  • BDecreasing eddy current loss
  • CDecreasing both hysteresis and eddy current loss
  • DManufacturing ease
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Correct Answer : (B)

Decreasing eddy current loss

Explanation:

Pole shoe of a dc machine is laminated for the purpose of Decreasing eddy current loss.

20.The function  of pole shoes in a dc machine is to

  • ASupport the field coils
  • BReduce the reluctance of the magnetic path
  • CSpread out the flux to achieve uniform flux distribution in the air gap
  • DAll of the above
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Correct Answer : (D)

All of the above

Explanation:

The function  of pole shoes in a dc machine is  to Support the field coils, Reduce the reluctance of the magnetic path, Spread out the flux to achieve uniform flux distribution in the air gap.