300 Important DC Motor MCQ Questions & Answers with Explanation | PDF Free Download
1.If the flux of a dc motor approaches zero, its speed will
- Aapproach infinity
- Bapproach zero
- Cremain unchanged
- Dbetween zero and infinity
2.A series motor is working drawing a load current of 1A from the line if now the load is reduced such that the current drawn is halved, the speed of the machine (neglecting the saturation and armature resistance) would be
- Aunchanged
- Breduced by 50%
- Creduced by 100%
- Dincreased by 100%
3.A dc shunt motor runs at rated speed. If its field circuit gets open circuited, then the motor speed would tend to
- ADecrease
- BRemain unchanged
- CIncrease
- DFluctuate around its previous speed
4.The speed of a dc shunt motor ____from no load to full load
- AFalls slightly
- BImproves slightly
- CRemains unchanged
- DFalls rapidly
5.A dc shunt generator has an armature resistance of 0.1 and runs at 1200 rpm when delivering 50 kW at 250 V. The speed of the machine, when run as a motor fed from 250 V supply and drawing 50 kW will be approximately.
- A1410 rpm
- B1020 rpm
- C1100 rpm
- D1320 rpm
6.A dc motor having full load speed of 750 rpm and speed regulation of 10% will have no load speed of
- A825 rpm
- B675 rpm
- C800 rpm
- D700 rpm
7.The mechanical power developed by a dc motor maximum is maximum when
- ABack emf is equal to applied voltage
- BBack emf is equal to zero
- CBack emf is equal to half the applied voltage
- DNone of the above
8.If the applied voltage to a dc machine is 230 V, then the back emf, for maximum power developed is
- A115 V
- B200 V
- C230 V
- D460 V
9.The efficiency of a dc motor when developing maximum power will be about
- A100%
- B50%
- CLess than 50%
- DMore than 50%
10.The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
- A4.0
- B2.0
- C0.5
- D0.25
11.The dc motor, which can provide zero speed regulation at full load without any controller is
- ASeries
- BShunt
- CCumulative compound
- DDifferential compound
12.A dc shunt motor having unsaturated magnetic circuit runs at 1,000rpm with rated voltage. If the applied voltage is half of the rated voltage, the motor will run at
- A2000 rpm
- B1000 rpm
- C750 rpm
- D500 rpm
13.What happens to the speed when the flux is reduced by 10% in a 200 V dc shunt motor having an armature resistance of 0.2 ohm carrying a current of 50 A and running at 960 rpm prior to weakening of field. The total torque may be assumed constant. Neglect losses
- A1250 rpm
- B1066 rpm
- C920 rpm
- D576 rpm
14.The torque developed in a dc series motor is
- AInversely proportional to armature current
- BDirectly proportional to armature current
- CDirectly Proportional to the square of armature current
- DProportional to the square root of the armature current
15.Torque developed by the armature of a dc motor is proportional to
- A(Back emf) x (Armature current)
- B(Magnetic flux per pole) x (Armature current)
- C(Back emf) x (Magnetic flux per pole)
- D(Back emf) / (Magnetic flux per pole)
16.What is the increase in torque expressed as percentage of initial torque, if the current drawn by a dc series motor is increased from 10A to 12A (neglect saturation)?
- A21%
- B25%
- C41%
- D44%
17.In an electric motor, the electromagnetic torque developed is
- AIn opposite direction to both load torque and frictional torque
- BIn the same direction as the load torque but in opposite direction to frictional torque
- CIn the same direction is the load torque and frictional torque
- DIn the same directional as the frictional torque but in the opposite direction to the load torque
18.The torque speed characteristic of a dc shunt motor is
- AA rectangular hyperbola
- BA drooping straight line
- CA parabola
- DNone of the above
19.The horse power obtained from the motor shaft is called the
- A1 HP
- BBHP
- CUseful output
- DNone of these
20.The shaft torque is less than armature torque in a dc motor. This is due to
- AEddy current loss
- BHysteresis loss
- CStray loss
- DAll of the above