Electrical Studys

 

1) In case of D.C. shunt motors the speed is dependent on back e.m.f. only because ______

1 pointA. back e.m.f. is equal to armature drop B. armature drop is negligibleC. flux is proportional to armature currentD. flux is practically constant in D.C shunt motors

2) In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be ____

1 pointA. almost negligible B. rated full-load currentC. less than full-load currentD. more than full-load current

3) These days D.C. motors are widely used in

1 pointA. pumping sets B. air compressorsC. electric tractionD. machine shops

4) By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?

1 pointA. Frame B. ShaftC. CommutatorD. Stator

5) In which of the following applications D.C. series motor is invariably tried?

1 pointA. Starter for a carB. Drive for a water pumpC. Fan motorD. Motor operation in A.C. or D.C.

6) In D.C. machines fractional pitch winding is used ____

1 pointA. to improve cooling B. to reduce copper lossesC. to increase the generated e.m.f. D. to reduce the sparking

7) A three point starter is considered suitable for ______

1 pointA. shunt motors B. shunt as well as compound motorsC. shunt, compound and series motorsD. all D.C. motors

8) In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be

1 pointA. 100% B. around 90%C. anywhere between 75% and 90% D. less than 50%

9) The ratio of starting torque to full-load torque is least in case of _____

1 pointA. series motors B. shunt motorsC. compound motors D. none of the above

10) In D.C. motor which of the following can sustain the maximum temperature rise?

1 pointA. Slip rings B. CommutatorC. Field windingD. Armature winding

11) Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ?

1 pointA. Lenz's law B. Faraday's lawC. Coloumb's lawD. Fleming's left-hand rule

12) Which of the following load normally needs starting torque more than the rated torque?

1 pointA. Blowers B. ConveyorsC. Air compressorsD. Centrifugal pumps

13) The starting resistance of a D.C. motor is generally _____

1 pointA. low B. around 500 QC. 1000 QD. infinitely large

14) The speed of a D.C. series motor is

1 pointA. proportional to the armature current B. proportional to the square of the armature current C. proportional to field current D. inversely proportional to the armature current

15) In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to ______

1 pointA. 100% of the previous value B. 50% of the previous valueC. 25% of the previous value D. 10% of the previous value

16) The current drawn by the armature of D.C. motor is directly proportional to ____

1 pointA. the torque requiredB. the speed of the motorC. the voltage across the terminalsD. none of the above

17) The power mentioned on the name plate of an electric motor indicates ____

1 pointA. the power drawn in kW B. the power drawn in kVAC. the gross powerD. the output power available at the shaft

18) Which D.C. motor has got maximum self loading property?

1 pointA. Series motor B. Shunt motorC. Cumulatively compounded 'motorD. Differentially compounded motor

19) Which D.C. motor will be suitable alongwith flywheel for intermittent light and heavy loads?

1 pointA. Series motor B. Shunt motorC. Cumulatively compounded motorD. Differentially compounded motor

20) If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens

1 pointA. nothing will happen to the motor B. this will make armature to take heavy current, possibly burning it C. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stressesD. motor will run at very slow speed

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