1) For the construction of the armature of a d.c. machine, the best suited material is
a. Cast iron
b. Silicon steel
c. Carbon
d. All of these
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2) In a d.c. machine, the form of armature reaction mmf is
a. Triangular
b. Sinusoidal
c. Saw tooth
d. Rectangular
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3) For low reluctance path for the flux in armature, the permeability of the material should be
a. High
b. Low
c. Both (a) and (b)
d. None of these
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4) In a d.c. machine, the eddy current losses mainly occurs in
a. Armature
b. Windings
c. Yoke
d. At brush contact
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5) The conductors which will cause distortion in the main field flux of d.c. machine are
a. Demagnetizing armature conductors
b. Cross magnetizing armature conductors
c. Both (a) and (b)
d. None of these
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6) If the brush shift angle is given in electrical degrees then for converting it into mechanical degree by using the relation
a. θelectrical / P
b. 2θelectrical / P
c. θelectrical / 2P
d. 2P / θelectrical
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7) A 6 pole wave wound d.c. generator has 460 armature conductors carrying armature current of 180 A. The armature reaction demagnetizing and cross magnetizing ampere turns per pole if brushes are shifted by 6 degree electrical from G.N.A are
a. 3220, 230
b. 3220, 260
c. 260, 3220
d. 230, 3220
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8) For neutralizing the demagnetizing effect of armature reaction, an extra number of winding turns are provided on each pole. To calculate number of extra turns per pole the equation used is
a. (ATd / I) * leakage coefficient
b. (ATd / I) / leakage coefficient
c. Leakage coefficient / (ATd / I)
d. (ATd / I)
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9) Due to the effect of armature reaction in d.c. machine, the value of generated voltage and flux per pole
a. Increases, decreases
b. Decreases, decreases
c. Decreases, increases
d. Increases, increases
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10) The armature reaction in d.c. machine causes distortion in the main field flux. This effect of armature reaction can be reduced by
a. Increasing the length of air gap
b. Decreasing the length of air gap
c. Increasing the number of poles
d. Decreasing the number of poles
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11) Two 4 pole d.c. machines of identical armature, one with wave winding and other with lap winding are wound. Then
a. The lap wound machine will have more generated voltage
b. Wave wound machine will have more generated voltage
c. Both will have same generated voltage
d. None of these
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Answer
Explanation
Related Ques
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ANSWER: Wave wound machine will have more generated voltage
Explanation:
No explanation is available for this question!
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12) The armature in d.c. machines are always placed on rotor
a. Otherwise commutation will not be possible
b. Otherwise there will not be any induced emf
c. Otherwise current will not flow
d. All of these
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13) In a d.c. machine, the commutator provides
a. Half wave rectification
b. Full wave rectification
c. Semi controlled rectification
d. Uncontrolled rectification
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14) To have perfect neutralization of armature mmf under the pole shoe, the ampere conductors of compensating winding must be
a. Not equal to the total armature ampere conductors under the pole shoe
b. Equal to the total armature ampere conductors under the pole shoe
c. Half of the total armature ampere conductors under the pole shoe
d. Twice of the total armature ampere conductors under the pole shoe
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Answer
Explanation
Related Ques
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ANSWER: Equal to the total armature ampere conductors under the pole shoe
Explanation:
No explanation is available for this question!
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15) Ampere turns per pole for compensating winding in d.c. machines is equal to
a. (pole arc / pole pitch) * armature ampere turns per pole
b. (pole pitch / pole arc) * armature ampere turns per pole
c. (pole arc / pole pitch) * total ampere conductors per pole
d. None of these
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Answer
Explanation
Related Ques
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ANSWER: (pole arc / pole pitch) * armature ampere turns per pole
Explanation:
No explanation is available for this question!
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16) The compensating windings are used to neutralize the armature reaction in d.c. machines. These windings are connected
a. Across armature
b. In series with armature
c. Both (a) and (b)
d. None of these
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17) The armature reaction effect in d.c. machines can be completely neutralized by using
a. Only compensating winding
b. Only interpoles
c. Both compensating winding and interpoles
d. None of these
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18) Practically in d.c. machines, it may happen that the emf induced in different parallel paths may not be same. This will cause inequality in brush arm currents and will give rise to copper losses. These effects can be avoided by using
a. Compensating windings
b. Interpoles
c. Equalizer rings
d. All of these
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19) In d.c. machines, equalizer connections are provided in
a. Only wave winding
b. Only lap winding
c. Both wave winding and lap winding
d. None of these
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20) If in the d.c machine, the reversal of current in the coil is faster than ideal or linear commutation then the commutation is said to be
a. Retarded commutation
b. Under commutation
c. Accelerated commutation
d. Ideal commutation
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21) In d.c. machines, the interpoles have tapering shape which results in
a. Simpler design
b. Reduction in the weight
c. Increase in acceleration of commutation
d. All of these
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22) The generating action and motoring action in d.c. motor is determined by
a. Fleming’s left hand rule, Fleming’s right hand rule
b. Both by Fleming’s left hand rule
c. Both by Fleming’s right hand rule
d. Fleming’s right hand rule, Fleming’s left hand rule
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Answer
Explanation
Related Ques
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ANSWER: Fleming’s right hand rule, Fleming’s left hand rule
Explanation:
No explanation is available for this question!
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23) In a practical motor, to reverse the direction of rotation
a. Reverse the direction of main field produced by the field winding
b. Reverse the direction of current passing through the armature is reversed
c. Either (a) or (b)
d. None of these
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24) A 220 V, d.c. motor draws an armature current of 20 A. Its armature resistance is 0.6 ohm. Then the induced emf in the motor will be
a. 195 V
b. 202 V
c. 208 V
d. 215 V
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25) If the flux is increased by 50% and speed is reduced by 50% of a d.c. motor (keeping the other parameters constant), then its back emf will become
a. 50 % of the original back emf
b. 0.75 % of the original back emf
c. 100 % of the original back emf
d. 150 % of the original back emf
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26) If Eb is the back emf of d.c. motor and V is the terminal voltage, then the condition for maximum power is
a. Eb = V
b. Eb = 2V
c. Eb = ( V / 2 )
d. Eb = V ∧ 2
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27) A 4 pole, lap wound d.c. motor drawing an armature current of 20 A has 360 conductors. If the flux per pole is 0.015 Wb then the gross torque developed by the armature of motor is
a. 10.23 N-m
b. 15.56 N-m
c. 17.17 N-m
d. 19.08 N-m
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28) If the no load speed of d.c. motor is 1350 rpm and full load speed is 1150 rpm, then its voltage regulation is
a. 11.56 %
b. 15.36 %
c. 17.39 %
d. 19.39 %
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29) As the load on d.c. motor increases, the current drawn by motor
a. Increases
b. Decreases
c. Remains same
d. None of these
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30) If the back emf of a d.c. motor is doubled and flux is halved (keeping other parameters constant) then its speed will become
a. Double of the original speed
b. Square of the original speed
c. Four times of the original speed
d. Half of the original speed
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31) Keeping the field excitation constant, the constant of proportionality between back emf and armature speed of d.c. motor is
a. Twice of the proportionality constant between developed torque and armature current
b. Half of the proportionality constant between developed torque and armature current
c. Same as that of proportionality constant between developed torque and armature current
d. None of these
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Answer
Explanation
Related Ques
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ANSWER: Same as that of proportionality constant between developed torque and armature current
Explanation:
No explanation is available for this question!
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32) D.C. shunt motor is also called as
a. Constant flux motor
b. Constant voltage motor
c. Variable voltage motor
d. Constant current motor
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33) The torque developed in d.c. shunt motor is
a. Directly proportional to the armature current
b. Directly proportional to the square of the armature current
c. Inversely proportional to the armature current
d. Inversely proportional to the square of armature current
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Answer
Explanation
Related Ques
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ANSWER: Directly proportional to the armature current
Explanation:
No explanation is available for this question!
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34) For a constant torque load, if the armature resistance of shunt motor is doubled (keeping the shunt field constant) then the armature current will
a. Double
b. Get halved
c. Remain same
d. None of these
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35) A 4 pole, 220 V, 10 H.P, d.c. shunt motor is rotating at a speed of 320 rpm. Then the developed useful torque is
a. 210.647 N-m
b. 215.547 N-m
c. 219.484 N-m
d. None of these
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36) If a shunt motor is started with its field winding open then
a. It will rotate at the same speed as that with its field winding closed
b. It will rotate at less speed as that with its field winding closed
c. It will rotate at dangerously high speed
d. None of these
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37) D.C. shunt motors are commonly used in
a. Cranes
b. Electric traction
c. Elevators
d. Lathe machines
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38) For d.c. series motor, if Ia is the armature current then the torque developed is
a. α Ia
b. α Ia2
c. α (1 / Ia2)
d. α (1 / Ia)
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39) Neglecting saturation, if the current drawn from by a d.c. series motor is increased from 15 A to 18 A, then the increase in the torque expressed as percentage of initial torque will be
a. 22 %
b. 33%
c. 44%
d. 56.78%
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40) A 4 pole 240 V, d.c. series motor has a wave wound armature with 180 conductors. The armature resistance and the field winding resistance are 0.10 ohm and 0.2 ohm respectively. If the motor is drawing 40 A current at 0.015 Wb flux per pole, then the speed under this condition is
a. 2533.3 rpm
b. 2644.4 rpm
c. 2756.9 rpm
d. 2987.6 rpm
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