D.C. Generators

11. According to Fleming's right-hand rule for finding the direction of induced e.m.f., when middle finger points in the direction of induced e.m.f., forefinger will point in the direction of

  1. motion of conductor
  2. lines of force
  3. either of the above
  4. none of the above

Correct answer: (B)
lines of force

12. An exciter for a turbo generator is a

  1. separately excited generator
  2. shunt generator
  3. series generator
  4. compound generator

Correct answer: (B)
shunt generator

13. Armature coil is short circuited by brushes when it lies

  1. along neutral axis
  2. along field axis
  3. in any of the above positions
  4. in none of the above positions

Correct answer: (A)
along neutral axis

14. Armature reaction in a generator results in

  1. demagnetisation of leading pole tip and magnetisation of trailing pole tip
  2. demagnetisation of trailing pole tip and magnetisation of leading pole tip
  3. damagnetising the center of all poles
  4. magnetising the center of all poles

Correct answer: (A)
demagnetisation of leading pole tip and magnetisation of trailing pole tip

15. Armature reaction of an unsaturated D.C. machine is

  1. crossmagnetising
  2. demagnetising
  3. magnetising
  4. none of above

Correct answer: (A)
crossmagnetising

16. As a result of armature reaction, the reduction in the total mutual air gap flux in a D.C. generator is approximately

  1. 40 percent
  2. 25 percent
  3. 10 percent
  4. 5 percent

Correct answer: (D)
5 percent

17. Brushes of D.C. machines are made of

  1. carbon
  2. soft copper
  3. hard copper
  4. all of above

Correct answer: (A)
carbon

18. Compensating windings are used in D.C. generators

  1. mainly to reduce the eddy currents by providing local short-circuits
  2. to provide path for the circulation of cooling air
  3. to neutralise the cross-magnetising effect of the armature reaction
  4. none of the above

Correct answer: (C)
to neutralise the cross-magnetising effect of the armature reaction

19. Copper brushes in D.C. machine are used

  1. where low voltage and high currents are involved
  2. where high voltage and small cur-rents are involved
  3. in both of the above cases
  4. in none of the above cases

Correct answer: (A)
where low voltage and high currents are involved

20. D.C. generator generally preferred for charging automobile batteries is

  1. series generator
  2. shunt generator
  3. long shunt compound generator
  4. any of'the above

Correct answer: (C)
long shunt compound generator

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