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1) In D.C. machines the number of slots per pole usually lies___________? a. between 2 to 4 b. between 6 to 8 c. between 9 to 16 d. between 20 to 30
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2) Which of the following methods may be adopted to reduce the effects of armature reaction ? a. Increase in length of air gap at pole tips b. Increasing reluctance of pole tips c. Compensating windings d. Interpoles e. All of the above
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3) In D.C. machines, the ________ in field mmf results in increase in size and cost of machines? a. increase b. decrease c. either of the above d. none of the above
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4) In D.C. machines the width of the duct is usually_____________? a. 4 mm b. 6 mm c. 8 mm d. 10 mm
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5) In a D.C. machine the current per brush arm should not be more than_____________? a. 100 A b. 200 A c. 300 A d. 400 A
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6) The weight of copper of both armature and field windings decreases with __________ in number of poles? a. increase b. decrease c. either of the above d. none of the above
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7) In a D.C. machine, the value of peripheral speed should not, normally, exceed___________? a. 10 m/s b. 20 m/s c. 30 m/s d. 40 m/s
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8) In D.C. machines, ir order to prevent excessive distortion of field form by the armature reaction, the field mmf must be made____________? a. equal to that of armature mmf b. less in comparison with the armature mmf c. large in comparison with the armature mmf d. none of the above
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9) The operation of a D.C. machine with large air gap lengths is comparatively_____________? a. quiet b. noisy c. either of the above d. none of the above
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10) In D.C. machines the usual limit of slot pitch is________________? a. between 5 to 10 mm b. between 10 to 15 mm c. between 15 to 20 mm d. between 25 to 35 mm
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11) D.C. machines designed with a large value of air gap length have_____________? a. worst, ventilation b. poor ventilation c. better ventilation d. none of the above
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12) In a D.C. machine the number of brush arms is _________ the number of poles? a. less than b. equal to c. greater than d. none of the above
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13) Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ? a. Increased I R losses b. Increased core losses c. Poor commutation d. Change in motor parameters e. All of the above
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14) Which of the following brushes can be used for high values of current density ? a. Metal graphite brushes b. Hard carbon brushes c. Electro-graphitic brushes d. Natural graphite brushes
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15) is usually used for brush rockers____________? a. Mild steel b. Copper c. Aluminium d. Cast-iron
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16) The stator of a D.C. machine comprises of_____________? a. main poles b. interpoles c. frame d. all of the above
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17) Which of the following in an application of D.C. motors? a. Traction b. Drives for process industry c. Battery driven vehicles d. Automatic control e. All of the above
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18) The cylindrical windings using circular conductors are used for current rating of____________? a. upto 20 A b. upto 40 A c. upto 60 A d. upto 80 A
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19) D.C. servomotors are used in______________? a. purely D.C. control systems b. purely AC. control systems c. both D.C. and AC. control systems d. none of the above
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20) The laminations of the armature of a D.C. machine are usually ___________ thick? a. 0.1 to 0.2 mm b. 0.2 to 0.3 mm c. 0.3 to 0.4 mm d. 0.4 to 0.5 mm
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