Quiz  /  D.C. Motors Gate & PSU MCQ Questions With Answers

  • 1. 
    You can tell that an electric motor is brushless because it has...

  • 1 wire attached to it.
  • 2 wires attached to it.
  • 3 wires attached to it.
  • No wires attached to it.

  • 2. 
    Which of the following is not a component of a stepper motor?

  • Windings
  • Rotor and Stator
  • Commutator
  • Brush
  • Both C and D

  • 3. 
    A wire XY lies between the poles of a magnet. The diagram shows the upward force on the wire XY caused when there is an electric current in the direction XY as shown.Three tests are made using this apparatus: 1 The current direction is reversed. 2 The N and S poles are swapped around. 3 The current is switched off.Which will result in no change in the size of the force on the wire?

  • 1 and 2 only
  • 1 only
  • 2 only
  • 3 only

  • 4. 
    The reason for using starter while starting of DC motor is

  • To restrict armature current as there is no back E.M.F at starting
  • Motors are not self-starting
  • Restrict starting torque
  • None of the above

  • 5. 
    In which of the following case we will get maximum power?

  • Ea = 2 x supply voltage
  • Ea = supply voltage
  • Supply voltage = 2 x Ea
  • supply voltage = 4 x Ea

  • 6. 
    Eddy current are induced in the pole shoes of a DC machine due to

  • Oscillating magnetic field
  • Pulsating magnetic flux
  • Relative rotation between field and armature
  • None of the above

  • 7. 
    Which description below best matches the symbol shown?

  • Control relay coil
  • Motor starter coil
  • Contactor coil
  • Indicating light

  • 8. 
    The starting resistance of D.C motor is generally

  • High
  • Infinite
  • Low
  • None of the above

  • 9. 
    A coil carries a current in a magnetic field. The coil experiences a turning effect.Which device uses this effect?

  • a DC motor
  • an electromagnet
  • a relay
  • a transformer

  • 10. 
    The shaft torque (Tsh) in a d.c motor is less than total armature torque (Ta) because of ……………. in the motor.

  • Copper losses
  • Field Losses
  • Iron and Friction losses
  • None of the above

  • 11. 
    Which of the following quantity will decrease if supply voltage is increased?

  • Starting torque
  • Operating speed
  • Full-load current
  • Cannot be determined

  • 12. 
    In DC motor, which of the following part can sustain the maximum temperature rise?

  • Field winding
  • Commutator
  • Slip rings
  • Armature winding

  • 13. 
    The torque developed by a d.c motor is directly proportional to

  • Flux per pole x Armature current
  • Armature resistance x Applied voltage
  • Armature Resistance x Armature current
  • Square of armature resistance

  • 14. 
    The value of back e.m.f in a DC motor is maximum at _______

  • No load
  • Full load
  • Half load
  • None of the above

  • 15. 
    The speed of DC motor is

  • Always constant
  • Directly proportional to back e.m.f
  • Directly proportional to flux
  • Inversely proportional to the product of back e.m.f and flux

  • 16. 
    The direction of rotation of D.C series motor can be changed by

  • Interchanging field terminal
  • Interchanging supply terminal
  • Both 1&2
  • None of the above

  • 17. 
    What will happen when the D.C motor is connected to A.C supply then?

  • D.C motor will run at rated speed
  • D.C motor will burn
  • D.C motor will run at slow speed
  • Both 2 & 3.

  • 18. 
    Counter EMF of the DC motor is

  • Less than the applied voltage
  • More than the applied voltage
  • Equal to the applied voltage
  • None of the above

  • 19. 
    A 4 pole, 250 V, dc series motor has a wave connected armature with 200 conductors. The flux per pole is 25 mWb when the motor is drawing 60 A from the supply. Armature resistance is 0.15 Ω while series field winding resistance is 0.2 Ω.Calculate the speed under this condition.

  • 1500 RPM
  • 1470 RPM
  • 1300 RPM
  • 1374 RPM

  • 20. 
    The speed of a DC motor is ________

  • Directly proportional to flux per pole
  • Inversely proportional to flux per pole
  • Inversely proportional to applied voltage
  • None of the above

  • 21. 
    The image shown is of a...

  • Internal combustion motor
  • Turbine engine
  • Brushed DC motor
  • Brushless AC motor

  • 22. 
    The field poles and armature of a DC machine are laminated to _________

  • Reduce the weight of the machine
  • Decrease the speed
  • Reduce eddy currents
  • Reduce armature reaction

  • 23. 
    A 250 V, DC shunt motor takes a line current of 20 A. Resistance of shunt field winding is 200Ω and resistance of the armature is 0.3 Ω Find the armature current and the back e.m.f.

  • 18.75 A, 245 V
  • 25.32 A, 225 V
  • 15.65 A, 100 V
  • 10 A, 150 V

  • 24. 
    A brushless motor is more efficient than a brushed motor because...

  • There is less energy lost inside the motor due to friction and heat.
  • There is less power used to spin the motor.
  • There is less noise created in spinning the motor.
  • This is an incorrect statement. Brushed motors are more efficient.

  • 25. 
    In case of parallel field connection, it won’t rotate at all and will start humming and will create vibrations, as a torque produced by positive and negative cycle will cancel out each other. DC motor will be heated up and it may burn.

  • Winding
  • Shaft
  • Commutator
  • Stator

  • 26. 
    The diagram shows a current-carrying wire placed between two magnetic poles. The current is in the direction shown.What is the direction of the force on the wire?

  • towards the bottom of the page
  • towards the top of the page
  • towards the left-hand side of the page
  • towards the right-hand side of the page
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