Electric Traction MCQ

41. Skidding of a vehicle always occurs when

(a) braking effort exceeds its adhesive weight.
(b) brake is applied suddenly.
(c) it negotiates a curve.
(d) it passes over points and crossings.

42. The adhesive weight is the

(a) total weight of the locomotive and the train.
(b) weight coming over the driving wheels.
(c) same as the accelerating weight.
(d) none of the above.

43. Coefficient of adhesion is the ratio of tractive effort to slip the wheels and

(a) dead weight.
(b) accelerating weight.
(c) adhesive weight.
(d) none of the above.

44. The normal value of coefficient of adhesion is

(a) 0.25
(b) 0.35
(c) 0.50
(d) 0.65

45. Coefficient of adhesion reduces due to the presence of

(a) dew on rails.
(b) oil and grease on rails.
(c) dry sand on rails.
(d) both (a) and (b).

46. Coefficient of adhesion improves due to presence of

(a) dry sand on rails.
(b) rust on rails.
(c) dust on rails.
(d) all of the above.

47. The value of coefficient of adhesion will be high when rails are

(a) wet.
(b) cleaned with sand.
(c) greased.
(d) sprayed with oil.

48. The coefficient of adhesion for wet or greasy rails is

(a) 0.35
(b) 0.25
(c) 0.08
(d) zero

49. The coefficient of adhesion

(a) same on dc and ac traction.
(b) high in ac traction and low in dc traction.
(c) high in dc traction and low in ac traction.
(d) any of the above.

50. Higher value of tractive effort can be used in electric traction as compared to steam traction because

(a) of greater adhesive weight (the weight on driving wheels is 70 percent of dead weight in case of electric locomotive whereas in case of steam locomotive it is 50 percent).
(b) the torque exerted in electric traction is continuous whereas in steam traction it is pulsating one.
(c) the driving wheels are distributed over a much greater length in electric traction whereas in steam traction they are close to each other.
(d) all of the above.

51. When a bogie negotiates a curve, reduction in adhesion occurs resulting in sliding. This sliding is acute when

(a) degree of curvature is more.
(b) wheel base of axles is more.
(c) none of the above.
(d) both (a) and (b).

52. For a given maximum axle load tractive effort with ac locomotive will be

(a) less than that of dc locomotive.
(b) more than that of dc locomotive.
(c) equal to that of dc locomotive.
(d) none of the above.

53. The resistance encountered by a train in motion is on account of

(a) resistance offered by air.
(b) friction at the track.
(c) friction at various parts of the rolling stock.
(d) all of the above.

54. The air resistance to the movement of the train is proportional to

(a) 1/speed.
(b) (speed).
(c) (speed)².
(d) (speed)³.

55. The friction at the track is proportional to

(a) speed.
(b) (speed)².
(c) (speed)³.
(d) (1/speed)².

56. If the resistance to electric train movement is given by F_r= a + bv + cv₂ In the above expression b is likely to cover

(a) air resistance.
(b) track resistance.
(c) frictional resistance.
(d) none of the above.

57. Tractive effort of an electric locomotive can be increased by

(a) using high output motors.
(b) increasing the supply voltage.
(c) increasing dead weight over the driving axles.
(d) both (a) and (c).

58. A locomotive with a mass of 50,000 kg on a track whose coefficient of adhesion is 20 per cent will produce a tractive effort of (approximately)

(a) 1 kN
(b) 100 kN
(c) 25 kN
(d) 250 kN

59. Energy consumption in propelling the train is required for

(a) accelerating of train mass.
(b) overcoming the gradient while moving up the gradient.
(c) overcoming the train resistance.
(d) all of the above.

60. Longer coasting period for a train results in

(a) higher schedule speed .
(b) lower specific energy consumption.
(c) higher retardation.
(d) higher acceleration.