1) In a D.C. shunt motor, speed is______________? a. independent of armature current b. directly proportional to the armature current c. proportional to the square of the current d. inversely proportional to the armature current
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2) A direct on line starter is used: for starting motors___________? a. up to 5 H.P b. up to 10 H.P c. up to 15 H.P d. up to 20 H.P
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3) What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? a. The motor will stop b. The motor will continue to run c. The armature may burn d. The motor will run noisy
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4) In case of D.C. shunt motors the speed is dependent on back e.m.f. only because____________? a. back e.m.f. is equal to armature drop b. armature drop is negligible c. flux is proportional to armature current d. flux is practically constant in D:C. shunt motors
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5) In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be_____________? a. almost negligible b. rated full-load current c. less than full-load current d. more than full-load current
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6) These days D.C. motors are widely used in____________? a. pumping sets b. air compressors c. electric traction d. machine shops
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7) By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor? a. Frame b. Shaft c. Commutator d. Stator
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8) In which of the following applications D.C. series motor is invariably tried? a. Starter for a car b. Drive for a water pump c. Fan motor d. Motor operation in A.C. or D.C
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9) In D.C. machines fractional pitch winding is used__________? a. to improve cooling b. to reduce copper losses c. to increase the generated e.m.f. d. to reduce the sparking
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10) A three point starter is considered suitable for______________? a. shunt motors b. shunt as well as compound motors c. shunt, compound and series motors d. all D.C. motors
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11) In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be______________? a. 100% b. around 90% c. anywhere between 75% and 90% d. less than 50%
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12) The ratio of starting torque to full-load torque is least in case of____________? a. series motors b. shunt motors c. compound motors d. none of the above
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13) In D.C. motor which of the following can sustain the maximum temperature rise? a. Slip rings b. Commutator c. Field winding d. Armature winding
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14) Which of the following law/rule can he used to determine the direction of rotation of D.C. motor ? a. Lenz’s law b. Faraday’s law c. Coloumb’s law d. Fleming’s left-hand rule
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15) Which of the following load normally needs starting torque more than the rated torque? a. Blowers b. Conveyors c. Air compressors d. Centrifugal pumps
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16) The starting resistance of a D.C. motor is generally_______________? a. low b. around 500 Q c. 1000 Q d. infinitely large
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17) The speed of a D.C. series motor is_____________? a. 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
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18) In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to a. 100% of the previous value b. 50% of the previous value c. 25% of the previous value d. 10% of the previous value e. none of the above
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19) The current drawn by the armature of D.C. motor is directly proportional to__________? a. the torque required b. the speed of the motor c. the voltage across the terminals d. none of the above
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20) The power mentioned on the name plate of an electric motor indicates____________? a. the power drawn in kW b. the power drawn in kVA c. the gross power d. the output power available at the shaft
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