# DMRC JE/SSC JE/CIL MT ELECTRICAL ENGINEERING IMPORTANT MCQ PART 6(DC MOTORS)

 1.The current drawn by the armature of D.C. motor is directly proportional to the torque required the speed of the motor the voltage across the terminals none of the above ANSWER : : the torque required
 2.The power mentioned on the name plate of an electric motor indicates the power drawn in kW the power drawn in kVA the gross power the output power available at the shaft ANSWER : : the output power available at the shaft
 3.The speed of a D.C. series motor is proportional to the armature current proportional to the square of the armature current proportional to field current inversely proportional to the armature current ANSWER : : inversely proportional to the armature current
 4.The ratio of starting torque to full-load torque is least in case of series motors shunt motors compound motors none of the above ANSWER : : shunt motors
5.In D.C. motor which of the following can sustain the maximum temperature rise?
Slip rings
Commutator
Field winding
Armature winding

 6.Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ? Lenz’s law Faraday’s law Coloumb’s law Fleming’s left-hand rule ANSWER : : Fleming’s left-hand rule
 7.The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is 4.0 2.0 1.0 0.5 ANSWER : : 0.5
 8.The condition for maximum power in case of D.C. motor is back e.m.f. = 2 x supply voltage back e.m.f. = 1/2 x supply voltage supply voltage = 1/2 x back e.m.f. supply voltage = back e.m.f. ANSWER : : back e.m.f. =1/2 x supply voltage
 9.In D.C. machines fractional pitch winding is used to improve cooling to reduce copper losses to increase the generated e.m.f. to reduce the sparking ANSWER : : to reduce the sparking
 10.For the same H.P. rating and full load speed, following motor has poor starting torque shunt series differentially compounded cumulatively compounded ANSWER : : differentially compounded
 11.The starting resistance of a D.C. motor is generally low around 500 ohm 1000 ohm infinitely large ANSWER : : low
 12.Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads? Series motor Shunt motor Cumulatively compounded motor Differentially compounded motor ANSWER : : Cumulatively compounded motor
 13.In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to 100% of the previous value 50% of the previous value 25% of the previous value 10% of the previous value ANSWER : : 25% of the previous value
 14.If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens nothing will happen to with motor this will make armature to take heavy current, possibly burning it this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses motor will run at very slow speed ANSWER : this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
15.In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
100%
around 90%
anywhere between 75% and 90%
less than 50%
ANSWER : : less than 50%

 16.In case of conductively compensated D.C. series motors, the compensating winding is provided as separately wound unit in parallel with armature winding in series with armature winding in parallel with field winding ANSWER : : in series with armature winding
 17.Which of the following load normally needs starting torque more than the rated torque? Blowers Conveyors Air compressors Centrifugal pumps ANSWER : : Conveyors
 18.Which D.C. motor has got maximum self loading property? Series motor Shunt motor Cumulatively compounded ‘motor Differentially compounded motor ANSWER : : Differentially compounded motor
19.A three point starter is considered suitable for
shunt motors
shunt as well as compound motors
shunt, compound and series motors
all D.C. motors
ANSWER : : shunt as well as compound motors

20.If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
Starting torque
Operating speed