DC Generator Objective Type Question Answer

60. If the flux per pole of a d.c. generator is halved but its speed is doubled, its generated e.m.f will

(i) be halved
(ii) remain the same
(iii) be doubled
(iv) be quadrupled

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61. Stray losses consist of

(i) magnetic and mechanical losses
(ii) magnetic and copper losses
(iii) mechanical and copper losses
(iv) none of the above

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62. Current-versus time graph for an ideal commutation is a

(i) straight line
(ii) parabola
(iii) hyperbola
(iv) none of the above

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63. The ideal commutation in a coil is not possible because each coil has

(i) resistance
(ii) inductance
(iii) capacitance
(iv) none of the above

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64. In Fig. 5, the electrical efficiency is

(i)VIa/(EgIa)
(ii) VIL/(EgIa)
(iii) EgIa/(VIa)
(iv) none of the above

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Figure 5

65. In Fig. 5, the overall efficiency will be

(i) less than electrical efficiency
(ii) more than electrical efficiency
(iii) equal to electrical efficiency
(iv) none of the above

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Figure 6

66. Fig. 6 shows the various power stages of a d.c. generator. The loss at A is

(i) iron loss
(ii) friction loss
(iii) iron and friction losses
(iv) none of the above

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67. In Fig. 6, the loss at B is

(i) iron loss
(ii) stray loss
(iii) friction loss
(iv) Cu loss

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68. In a d.c. generator, the main function of compensating winding is to

(i) assist in commutation
(ii) reduce demagnetizing effect of armature reaction.
(iii) reduce distorting effect of armature reaction
(iv) eliminate reactance voltage

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69. The efficiency of a d.c. generator means its

(i) electrical efficiency
(ii) overall efficiency
(iii) mechanical efficiency
(iv) none of the above

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70. The overall efficiency of a d.c. generator is maximum when its variable loss is equal to

(i) constant loss
(ii) stray loss
(iii) iron loss
(iv) mechanical loss

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71. In d.c. shunt generator, the constant losses is equal to

(i) stray losses
(ii) mechanical losses
(iii) stray losses plus shunt Cu loss
(iv) none of the above

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72. A 4-pole, lap-wound d.c. shunt generator has an armature winding consisting of 220 turns each of 0.004 Ω. The armature resistance is

(i) 0.5 Ω
(ii) 1 Ω
(iii) 0.025 Ω
(iv) 0.055 Ω

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73. In a long-shunt compound-wound generator, the shunt field is connected in parallel with

(i) armature
(ii) series field
(iii) parallel combination of armature and series field.
(iv) series combination of armature and series field

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74. Wave-wound generators provide

(i) less current but more voltage
(ii) more current but less voltage
(iii) more current and more voltage
(iv) none of the above

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75. The commutator of a d.c. generator acts as

(i) an amplifier
(ii) a rectifier
(iii) a load
(iv) none of the above

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76. In a d.c. generator, the eddy current power loss is

(i) directly proportional to thickness of each lamination
(ii) inversely proportional to thickness of each lamination
(iii) directly proportional to square of thickness of each lamination
(iv) none of the above

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77. In a practical d.c. generator, mechanical efficiency is

(i) less than electrical efficiency
(ii) more than electrical efficiency
(iii) equal to electrical efficiency
(iv) none of the above

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78. In a d.c. generator, the relation among mechanical efficiency (ɳm), electrical efficiency (ɳe) and overall efficiency (ɳo) is

(i) ɳo = ɳm x ɳe
(ii) ɳo = ɳme
(iii) ɳo = ɳem
(iv) none of the above

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79. The armature copper loss in a d.c. generator is a

(i) constant loss
(ii) variable loss
(iii) stray loss
(iv) none of the above

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80. The armature reaction in a d.c. generator can be increased by increasing the

(i) field current
(ii) armature current
(iii) data is insufficient
(iv) none of the above

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