MSBTE I Scheme Practice MCQs of “Element of Electrical Engineering (22215)” All Chapter MCQ UNIT-4. Transformer and DC Motor.

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MSBTE I Scheme Practice MCQs of “Element of Electrical Engineering (22215)”

 

UNIT-4. Transformer and DC Motor.

 

1. Which of the following is minimized by laminating the core of a electrical transformers?

  1. Hysteresis loss
  2. Eddy current loss
  3. Heat loss
  4. All of the above

Answer: ( 2 )

 

2. The function of breather in electrical transformers is

  1. To provide oxygen to the cooling oil
  2. To provide coling air
  3. To arrest flow of moisture when outside air enters the transformer
  4. To filter the transformer oil

Answer: ( 3 )

 

3. Iron loss in a transformer occurs in

  1. Core
  2. Winding
  3. Insulating oil
  4. Main body

Answer: ( 1 )

 

4. Under no load conditions, which of the following loss is negligible?

  1. Hysteresis loss
  2. Eddy current loss
  3. Copper loss
  4. All losses have same magnitude

Answer: ( 3 )

 

5. Open circuit test of a electrical transformers gives

  1. Hysteresis loss
  2. Eddy current loss
  3. Sum of hysteresis and eddy current loss
  4. Copper loss

Answer: ( 3 )

 

6. Copper loss in a electrical transformers occurs in

  1. Core
  2. Winding
  3. Main body
  4. Bushings

Answer: ( 2 )

 

7. Which test of a transformer provides information about regulation, efficiency and heading under load conditions?

  1. Open circuit test
  2. Back to back test
  3. Hopkinson test
  4. Short circuit test

Answer: ( 2 )

 

8. For a transformer, the condition for maximum efficiency is

  1. Hysteresis loss = Eddy current loss
  2. Core loss = Hysteresis loss
  3. Copper loss = Iron loss
  4. Total loss = 2/3 of copper loss

Answer: ( 3 )

 

9. Eddy current losses in a transformer core can be reduced by

  1. Reducing the thickness of laminations
  2. Increasing the thickness of laminations
  3. Increasing the air gap in the magnetic circuit
  4. Reducing the airgap in the magnetic circuit

Answer: ( 1 )

 

10. When Rs is the resistance of secondary winding of the transformer and K is the transformation ratio, the equivalent secondary resistance as referred to primary side is given by

  1. K.Rs^2
  2. K^2.Rs
  3. Rs/K
  4. Rs/K^2

Answer: ( 4 )

 

11. In a transformer, the magnetic coupling between the primary and secondary circuit can be increased by

  1. Increasing the number of turns
  2. Using soft material for windings
  3. Using the magnetic core of low reluctance
  4. Using transformer oil for better quality

Answer: ( 3 )

 

12. If flux density in the core of the electrical transformers are increased

  1. Freuency on secondary winding will change
  2. Wave shape on secondary side will be distorted
  3. Size of the transformer will be reduced
  4. Eddy current losses will reduce

Answer: ( 3 )

 

13. Which loss in a tranformer varies significally with load?

  1. Hysteresis loss
  2. Eddy current loss
  3. Copper loss
  4. Core loss

Answer: ( 3 )

 

14. Voltage remaining constant, if the frequency is increased then

  1. Eddy current loss will decrease
  2. Hysteresis losses will decrease
  3. Eddy current losses will remain unchanged
  4. Hysteresis losses will remain unchanged

Answer: ( 3 )

 

15. The power factor of a transformer

  1. Is always unity
  2. Is always leading
  3. Is always lagging
  4. Depends on power factor of the load

Answer: ( 4 )

 

DC Motor MCQ

 

1) Brushes of DC Motors are made of

  1. Carbon
  2. Soft carbon
  3. Hard carbon
  4. Aluminium

Answer: ( 1 )

 

2) Armature reaction of an unsaturated DC machine is

  1. Cross-magnetizing
  2. Demagnetizing
  3. Magnetizing
  4. None of the above

Answer: ( 1 )

 

3) Eddy current are induced in the pole shoes of a DC machine due to

  1. Oscillating magnetic field
  2. Pulsating magnetic flux
  3. Relative rotation between field and armature
  4. None of the above

Answer: ( 1 )

 

4) In a DC machine, short circuited field coil will result in

  1. Odour of baring insulation
  2. Unbalanced magnetic pull producing vibrations
  3. Reduction of generated voltage for which excitation has to be increased to maintain the voltage
  4. All of the above

Answer: ( 4 )

 

5) In a DC machine, fractional pitch winding is used

  1. To increase the generated voltage
  2. To reduce sparking
  3. To save copper because of short end connection
  4. Due to both 2 and 3

Answer: ( 4 )

 

6) A DC motor is used in industrial application because it ________

  1. Is cheap
  2. Is simple in construction
  3. Provide fine speed control
  4. None of the above

Answer: ( 3 )

 

7) The field poles and armature of a DC machine are laminated to _________

  1. Reduce the weight of the machine
  2. Decrease the speed
  3. Reduce eddy currents
  4. Reduce armature reaction

Answer: ( 3 )

 

8) The back emf in a DC motor _______

  1. Opposes the applied voltage
  2. Aids the applied voltage
  3. Aids the armature current
  4. None of the above

Answer: ( 1 )

 

9) The value of back e.m.f in a DC motor is maximum at _______

  1. No load
  2. Full load
  3. Half load
  4. None of the above

Answer: ( 1 )

 

10) The motor equation is given by

  1. V = Eb – IaRa
  2. V = Eb + IaRa
  3. Eb = IaRa – V
  4. none of the above

Answer: ( 2 )

 

11) The fully loaded current of a 20 HP 500 V DC motor will be closer to

  1. 100 A
  2. 60 A
  3. 35 A
  4. 15 A

Answer: ( 3 )

 

12) The speed of a DC motor can be varied by varying

  1. Field current
  2. Applied voltage
  3. Resistance in series with armature
  4. Any of the above

Answer: ( 4 )

 

13) In a DC motors, the conditions for maximum power is

  1. Supply voltage = 1/2 × back e.m.f
  2. Supply voltage = √2 × back e.m.f
  3. Back e.m.f = 2 × supply voltage
  4. Back e.m.f = 1/2 × supply voltage

Answer: ( 4 )

 

14) If conditions for maximum power for a DC motor are established, the efficiency of the motor will be

  1. 100%
  2. 90 to 95%
  3. 81%
  4. Less than 50%

Answer: ( 4 )

 

15) When the speed of a DC motor increases, its armature current _______

  1. Increases
  2. Decreases
  3. Remains constant
  4. None of the above

Answer: ( 2 )

 

16) The amount of back e.m.f of a shunt motor will increase when _________

  1. The load is increased
  2. The field is weakened
  3. The field is strengthened
  4. None of the above

Answer: ( 3 )

 

17) The speed of a DC motor is ________

  1. Directly proportional to flux per pole
  2. Inversely proportional to flux per pole
  3. Inversely proportional to applied voltage
  4. None of the above

Answer: ( 2 )

 

18) A 200 V DC machine has an armature resistance of 0.5 Ω. If the full armature current is 30 A, the induced e.m.f when the machine acts as (i) generator (ii) motor, will be

  1. 170 V, 230 V
  2. 175 V, 225 V
  3. 185 V, 215 V
  4. 215 V, 185 V

Answer: ( 4 )

 

19) The ratio of starting torque to fully load torque is least in case of

  1. Shunt motors
  2. Series motors
  3. Compound motors
  4. Differential compound motor

Answer: ( 1 )

 

20) The speed of DC motor is

  1. Always constant
  2. Directly proportional to back e.m.f
  3. Directly proportional to flux
  4. Inversely proportional to the product of back e.m.f and flux

Answer: ( 2 )

 

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1 Comments

  1. UnknownMarch 8, 2021 at 2:27 PM

    Engineering metrology (mechanical engineering 3 semester) I scheme.

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