D.C. Motors MCQ

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• For a D.C. shunt motor if the excitation is changed
  ক

  Torque will remain constant

  খ

  Torque will change but power will remain constant

  গ

  Torque and power both will change

  ঘ

  Torque, power and speed, all will change
• If a D.C. motor is to be selected for conveyors, which motor would be preferred ?
  ক

  Series motor

  খ

  Shunt motor

  গ

  Differentially compound motor

  ঘ

  Cumulative compound motor
• If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
  ক

  Regenerative

  খ

  Plugging

  গ

  Dynamic braking

  ঘ

  None of the above
• In variable speed motor
  ক

  A stronger commutating field is needed at low speed than at high speed

  খ

  A weaker commutating field is needed at low speed than at high speed

  গ

  Same commutating field is needed at low speed than at high speed

  ঘ

  None of the above is correct
• In D.C. motor which of the following can sustain the maximum temperature rise?
  ক

  Slip rings

  খ

  Commutator

  গ

  Field winding

  ঘ

  Armature winding
• D.C. generators are normally designed for maximum efficiency around
  ক

  Full load

  খ

  Rated r.p.m.

  গ

  Rated voltage

  ঘ

  All of the above
• The power mentioned on the name plate of an electric motor indicates
  ক

  The power drawn in kW

  খ

  The power drawn in kVA

  গ

  The gross power

  ঘ

  The output power available at the shaft
• No-load speed of which of the following motor will be highest?
  ক

  Shunt motor

  খ

  Series motor

  গ

  Cumulative compound motor

  ঘ

  Differentiate compound motor
• In D.C. shunt motors as load is reduced
  ক

  The speed will increase abruptly

  খ

  The speed will increase in proportion to reduction in load

  গ

  The speed will remain almost/constant

  ঘ

  The speed will reduce
• These days D.C. motors are widely used in
  ক

  Pumping sets

  খ

  Air compressors

  গ

  Electric traction

  ঘ

  Machine shops
• Three point starter can be used for
  ক

  Series motor only

  খ

  Shunt motor only

  গ

  Compound motor only

  ঘ

  Both shunt and compound motor
• Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors?
  ক

  Low cost

  খ

  Wide speed range

  গ

  Stability

  ঘ

  High starting torque
• D.C. series motors are used
  ক

  Where load is constant

  খ

  Where load changes frequently

  গ

  Where constant operating speed is needed

  ঘ

  In none of the above situations
• The main disadvantage of the Ward-Leonard control method is
  ক

  High initial cost

  খ

  High maintenance cost

  গ

  Low efficiency at high loads

  ঘ

  All of the above
• If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
  ক

  Nothing will happen to the motor

  খ

  This will make armature to take heavy current, possibly burning it

  গ

  This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

  ঘ

  Motor will run at very slow speed
• If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
  ক

  This will make armature to take heavy current, possibly burning it

  খ

  This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

  গ

  Nothing will happen to motor

  ঘ

  Motor will come to stop
• What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
  ক

  The motor will stop

  খ

  The motor will continue to run

  গ

  The armature may burn

  ঘ

  The motor will run noisy
• The armature torque of the D.C. shunt motor is proportional to
  ক

  field flux only

  খ

  armature current only

  গ

  both (A) and (B)

  ঘ

  none of the above
• Which D.C. motor is generally preferred for cranes and hoists?
  ক

  Series motor

  খ

  Shunt motor

  গ

  Cumulatively compounded motor

  ঘ

  Differentially compounded motor
• For the same H.P. rating and full load speed, following motor has poor starting torque
  ক

  Shunt

  খ

  Series

  গ

  Differentially compounded

  ঘ

  Cumulatively compounded
• At the instant of starting when a D.C. motor is put on supply, it behaves like
  ক

  A highly resistive circuit

  খ

  A low resistance circuit

  গ

  A capacitive circuit

  ঘ

  None of the above
• Differentially compound D.C. motors can find applications requiring
  ক

  High starting torque

  খ

  Low starting torque

  গ

  Variable speed

  ঘ

  Frequent on-off cycles
• If the supply voltage for a D.C. motor is increased, which of the following will decrease?
  ক

  Starting torque

  খ

  Operating speed

  গ

  Full-load current

  ঘ

  All of the above
• Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be
  ক

  Level compounded

  খ

  Under compounded

  গ

  Cumulatively compounded

  ঘ

  Differentially compounded
• Which motor has the poorest speed control?
  ক

  Differentially compounded motor

  খ

  Cumulatively compounded motor

  গ

  Shunt motor

  ঘ

  Series motor
• The direction of rotation of a D.C. series motor can be changed by
  ক

  Interchanging supply terminals

  খ

  Interchanging field terminals

  গ

  Either of (A) and (B) above

  ঘ

  None of the above
• In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
  ক

  100%

  খ

  Around 90%

  গ

  Anywhere between 75% and 90%

  ঘ

  Less than 50%
• Which of the following losses are significantly reduced by laminating the core of a D.C. generator?
  ক

  Hysteresis losses

  খ

  Eddy current losses

  গ

  Copper losses

  ঘ

  Windage losses
• The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
  ক

  4.0

  খ

  2.0

  গ

  1.0

  ঘ

  0.5
• Which of the following motors is most suitable for signalling devices and many kinds of timers ?
  ক

  D.C. shunt motor

  খ

  D.C. series motor

  গ

  Induction motor

  ঘ

  Reluctance motor